Locked iphone

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 an iPhone or iPad 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 - Apple Support

No I don't have your Apple ID, this is a user to user forum, we are all iPhone users just like you. It's not that hard to follow the directions, just take one step at a time.

If you still don't feel comfortable doing it, make an appointment at an Apple Genius Bare and they can help -

Genius Bar Reservation and Apple Support Options - Apple

And.....the grandson now can't remember the password......correct?

Unfortunately, this is going to be a painful experience.