iPhone unavailable

To unlock your iPhone, follow the steps described in the Apple article:

(< iOS 15.2) ->: If you forgot your iPhone passcode

If you forgot your iPhone passcode - Apple Support

(iOS 15.2 or iPadOS 15.2 and newer) If you see an iPhone or iPad unavailable message or Security Lockout screen

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

If your iPhone is locker for a extremely long time and you have a Mac, plug the phone in to the mac then follow the iTunes restoration process