Open run with "Start + R", then open "shell:startup". it opens you a folder(the folder that was mentioned before at start menu), and every file that is on this folder, well run at startup.
The folder path is: "C:\Users\USERNAME\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup" (you can copy it on windows explorer, or copy this path and put your account name on USERNAME)
this is the trick i used in my script:
from os import getcwd
from shutil import copy
copy(getcwd()+'/FILE_NAME.exe','C:/Users/USERNAME/AppData/Roaming/Microsoft/Windows/Start Menu/Programs/Startup')
They are some ways for file name as well, but im not familiar with it. this code copies it self to startup folder and starts each time windows boots