how to restore iphone 12

It won't hurt to try a Forced Restart.....but it probably won't help either. This is the first thing that a tech will try if you take the phone in for service.

Force restart iPhone - Apple Support

There are only 2 possible results when you perform a Forced Restart:

1) The phone returns to normal operation.....unlikely, but possible

or else.....

2) There is a hardware problem with the phone that will need attention at the Apple Store (make an appointment) or at an authorized Apple Service shop.

You can find a list of authorized service locations using this link:

Find Locations