The next two steps demonstrate the iSclack, a handy tool that we recommend for anyone doing frequent repairs. If you aren't using the iSclack, skip down two steps for an alternate method.
If the plastic depth gauge is attached at the center of the iSclack, remove it now—it's not needed for larger iPhones like the iPhone 12.
Position the suction cups near the bottom edge of the iPhone—one on the front, and one on the back.
Press both suction cups firmly into place.