You can't really do that, but there are other means:
Enable find my phone, Enable remote wipe and change 6 digits passcode for alphanumeric one (8 characters or more - don't focus on special characters, instead use two-threee random words, longer the better)
https://xkcd.com/936/
Fingerprint reader is a convenience, not security.
Enable pin requirements very often and always with power-off press.