While holding the iPhone down with one hand, pull up on the suction cup to slightly separate the front panel assembly from the rear case.

Take your time and apply firm, constant force. The display assembly is a much tighter fit than most devices.

Using a plastic opening tool, begin to gently pry the rear case down, away from the display assembly, while continuing to pull up with the suction cup.

There are several clips attaching the front panel assembly to the rear case, so you may need to use a combination of the suction cup and plastic opening tool to free the front panel assembly.