Delete unknown fingerprints from iPhone or iPad
If there are multiple fingerprints on your iPhone or iPad and you want to remove the possibility that someone else can access your device using an additional fingerprint, you can reset fingerprints so that only your fingerprint is available on the device.
Go to Settings
> Touch ID & Passcode.If more than one fingerprint is available, place a finger on the Home button to identify its print.
Tap the fingerprint, then do any of the following:
Enter a name (such as “Thumb”).
Tap Delete Fingerprint.