Repair is only available "after" login and the play button is lit up , then if it detected a file issue the repair button will be available, if it doesn't detect an issue then no repair is possible
See https://answers.ea.com/t5/General-Discussion-Technical/GUIDE-Client-Repair-Scan/m-p/6454174#M70804
If your talking the original post in that link that is likley a antivirus or windows file protection issue hence failure to access content and write operations due to being blocked , not a swtor issue
I would suggest installing via steam https://help.ea.com/in/help/star-wars/star-wars-the-old-republic/swtor-on-steam/
Then repairing is done via steam itself https://help.steampowered.com/en/faqs/view/0C48-FCBD-DA71-93EB
Not with steam, the client repair is disabled, repair is done via steam file verification
And what for players that don't play on Steam?
For non steam, after login if the client detects an issue it will offer a repair otherwise it doesn't allow a repair as it doesn't see anything to fix
