Hello, try these steps:
1. Go to Settings, click Touch ID & Passcode, enter your passcode. Then turn off iTunes & App Store. Reboot your iPhone or iPad. Go back to Touch ID & Passcode in Settings and turn iTunes & App Store back on. Tap on Add a Fingerprint to add another fingerprint.
2. Remove and re-add fingerprints: Settings > Touch ID & Passcode > Enter the passcode of your device > Scroll down to find fingerprints. Tap on the fingerprint, which you want to delete and then Tap on Delete.
3. Force Restart your iPhone or iPad: Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears.
4. If a restart does not help try a Restore. First back up your iPhone using iTunes. Then connect your iDevice to computer and launch iTunes to restore your iPhone.