If you just want to reset your backup password in case the fingerprint scanner doesn't work, I am sure that should be straightforward, although I don't have one.
Someone will confirm for sure, but can you change from finger scan unlock to swipe unlock in Security without needing the backup password. What happens when you change back to fingerprint to unlock.
The Google account help pages (on a pc browser is best) are usually good at helping recover forgotten passwords with your memorable information.
Let us know if that doesn't work and someone more hands on will help.