iPhone unavailable

without deleting the data?

Is not possible, if you don't have a back up.

(< iOS 15.2) See this Apple article: If you forgot your iPhone passcode

If you forgot your iPhone passcode - Apple Support

(iOS 15.2 and newer) 

How to remove your iPhone, iPad, or iPod touch passcode without a computer

How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

If you didn't forget the passcode, how is the the phone unavailable?