There are early Greek texts that omit this troublesome "second-first" word. Other scholars think a scribe made an error with this word.
In any case, it appears in some later manuscripts. Here are some of these manuscripts available online.
Some Greek Texts deal with Luke 6:1 and the "second-first" Sabbath. Some early manuscripts do not have the troublesome verse.
Nestle 1904
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was going through the seedbeds, and his disciples were gathering the ears of corn in their hands.
Westcott and Hort 1881
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was going through the seedbeds, and his disciples were gathering the ears of corn in their hands.
Westcott and Hort / [NA27 and UBS4 variants]
Ἐγένετο δὲ ἐν σαββάτῳ διορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was going through the seedbeds, and his disciples were gathering the ears of corn in their hands.
Byzantine Byzantine Majority Text 2005
Ἐγένετο δὲ ἐν σαββάτῳ**
δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας, καὶ ἤσθιον, ψώχοντες ταῖς χερσίν.
And it came to pass on the second sabbath, that he journeyed through the seedbeds: and his disciples cast out the ears of grain, and the flesh, washing them with their hands.
Greek Orthodox Church
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσί.
And it came to pass on the second sabbath, that he went about sowing seeds;
Tischendorf 8th Edition
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσίν.
And it came to pass on the second sabbath, that he journeyed through the seedbeds, and his disciples gathered the ears of grain and flesh into their hands.
Scrivener's Textus Receptus 1894
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας, καὶ ἤσθιον, ψώχοντες ταῖς χερσί.
And it came to pass on the second sabbath, that he went forth through the seedbeds: and his disciples cast out the ears of grain, and the flesh, and dried them.
Stephanus Textus Receptus 1550
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσίν
And it came to pass on the second sabbath, that he went forth through the seedbeds, and his disciples plucked the ears of grain, and, gathering flesh in their hands
Greek Study Bible (Apostolic / Interlinear)**
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it came to pass on the sabbath day, that he went about sowing seeds, and his disciples gathered the ears of grain in their hands.
Here are some more Greek Tezts of Luke 6:1. Some omit the word entirely and others have the "second" Sabbath translated and not the second-first.
Berean Greek New Testament 2016
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
SBL Greek New Testament 2010
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
Nestle Greek New Testament 1904
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
Westcott and Hort 1881
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
Westcott and Hort / [NA27 variants]
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
Westcott and Hort / {NA28 variants}
Ἐγένετο δὲ ἐν σαββάτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ καὶ ἤσθιον τοὺς στάχυας ψώχοντες ταῖς χερσίν.
And it happened on the sabbath that he was traveling through the fields, and his disciples were gathering the ears of corn in their hands.
RP Byzantine Majority Text 2005
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας, καὶ ἤσθιον, ψώχοντες ταῖς χερσίν.
And it came to pass on the second sabbath, that he journeyed through the seedbeds: and his disciples cast out the ears of grain, and the grain, washing them with their hands.
Greek Orthodox Church 1904
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσί.
And it came to pass on the second sabbath, that he went about sowing seeds;
Tischendorf 8th Edition 1872
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ σπορίμων, καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσίν.
And it came to pass on the second sabbath, that he journeyed through the seedbeds, and his disciples gathered the ears of grain and flesh into their hands.
Scrivener's Textus Receptus 1894
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας, καὶ ἤσθιον, ψώχοντες ταῖς χερσί.
And it came to pass on the second sabbath, that he went forth through the seedbeds: and his disciples cast out the ears of grain, and the grain, and dried them.
Stephanus Textus Receptus 1550
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας καὶ ἤσθιον ψώχοντες ταῖς χερσίν
And it came to pass on the second sabbath, that he went forth through the seedbeds, and his disciples plucked the ears of corn, and gathered flesh into their hands.
Beza Greek New Testament 1598
Ἐγένετο δὲ ἐν σαββάτῳ δευτεροπρώτῳ διαπορεύεσθαι αὐτὸν διὰ τῶν σπορίμων· καὶ ἔτιλλον οἱ μαθηταὶ αὐτοῦ τοὺς στάχυας, καὶ ἤσθιον, ψώχοντες ταῖς χερσί.
And it came to pass on the second sabbath, that he went forth through the seedbeds: and his disciples cast out the ears of grain, and the grain, and dried them.