You can use the Help action to give an ally advantage on an ability check.
The Help action is what you are looking for:
You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next ability check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.
Telekinesis says:
You can try to move a Huge or smaller creature. Make an ability check with your spellcasting ability contested by the creature's Strength check. [...]
On subsequent rounds, you can use your action to attempt to maintain your telekinetic grip on the creature by repeating the contest.
So the NPC ally would use the Help action on their turn, and the target of telekinesis would have advantage on the next Strength check contest for the spell. Note, most DMs, myself included, would rule that the helping character has to be within reach of the helped character at the time of the ability check.
Helping on subsequent rounds
This will be the most common use case, I think. BBEG casts telekinesis on the paladin, we'll call him Rick.
After Rick's turn, it is Laurie's turn. She moves next to Rick and uses the Help action to help Rick escape telekinesis. On BBEG's turn, BBEG uses their action to maintain control of Rick. With Laurie's help, Rick has advantage on the strength check to be free from the telekinesis.
Helping with the initial check
This situation is a bit odd. From a purely mechanical perspective it works out just fine. On Laurie's turn, she moves next to Rick and declares "I'm using the help action to help Rick break free of a telekinesis spell, should one come his way." Then, if BBEG casts telekinesis on Rick, he has advantage on the initial strength check.
But this is a bit of an odd scenario. It takes some forward thinking from Laurie, which may not make sense if she is unaware of the BBEG's telekinetic capabilities. If she is totally unaware of the BBEG's ability to cast telekinesis, from a roleplaying perspective, it's probably much more likely that Laurie spends her action doing something else.
On the other hand, suppose Laurie knows BBEG is inclined to shaking his enemies about with some telekinesis. Then it may seem reasonable for Laurie to preemptively declare that she is going to Help Rick.