My son forgot his password on his IPhone. I don’t want to reset everything. What can we do?

Unfortunately, it's too late to recover the data on the phone.

If your iPhone is running iOS 15.2 or higher........you can use the instructions linked just below:

How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

If your iPhone is not running iOS 15.2 or higher........please use the instructions linked below, but note that you must use a PC or Mac.

If you forgot your iPhone passcode - Apple Support

If you have a backup of the phone, you can use the backup to restore the data on the phone during the new setup.

You need to restore it then reload your most recent backup. See if this helps: If you forgot your iPhone passcode - Apple Support

Might be a good idea to write down the new passcode and keep it in a safe place, even though you may feel that the new passcode will never be forgotten.