It would help to know if you have tried resetting your fingerprint, yes or no?
If yes and you simply cannot get your phone to accept a new one after several attempts there could possibly be a hardware issue with the fingerprint sensor itself. Or it could also just be a matter where if you restart your phone and try again that will work out.
If no, just go into your Settings >> Security >> Fingerprint and tap the Trash icon on the right side, then use the 'Add fingerprint' option to get a working fingerprint again.