You may be able to reset your backup PIN via your Samsung account; otherwise, you’ll probably need to factory reset, the unavoidably high price to pay for forgetting. All your personal data not backed up would be lost.
The fingerprint sensor may be simply repairable - a bad connection or something - so consider that possibility first.
Welcome to Android Central! Your backup password/PIN is very important -- it should never be brushed aside as something you think you'll never use. Android devices will typically ask for your backup password from time to time, even if you're successfully using your fingerprint sensor, because it adds extra security.