I forgot my password

Face ID requires a passcode entry every few days.

If you no longer remember your passcode, you can reset your iPhone.

With PC or Mac: If you forgot your iPhone passcode, use your Mac or PC to reset it - Apple Support

Without: If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

Face ID supports adding an alternate appearance, as well: Set up Face ID on iPhone - Apple Support

If you forgot the passcode on your iPhone, or your iPhone is disabled or unavailable -

Click on the link for instructions on how to reset your passcode without a computer if you have iOS 15.2 or higher.

If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

Click on the link for instructions on how to reset your passcode using a computer.

If you forgot your iPhone passcode, use your Mac or PC to reset it - Apple Support

If you don't know your passcode, don't make a lot of guesses hoping to get it right.

If you make enough bad guesses, you might trigger a security lockout that will force you to erase your phone to get back in. Then anything that hasn't been saved (e.g., in an iCloud backup; through iCloud synchronization) would be lost.