How do I resolve the 'passcode expired' issue on my iPhone?

My phone keeps popping up, saying passcode expired. Your phone unlock passcode has expired change passcode when I click change passcode it says passcode requirement to change your passcode. First answer your current passcode. I enter my passcode, which is the same one. I used to login in here and it won’t work and it keeps popping up.

[Re-Titled by Moderator]