This was challenging. For me, the suction cup could only create a tiny bit of motion and at first, no actual gap at all. You might have to pull the suction cup away from the base a few times just to loosen things up a tiny bit. Eventually, I got my fingernail in, and then after a few minutes got the plastic tool in.

Also, use the plastic tool to gently pry along the sides of the phone once there’s light there. I was afraid of using too much leverage and breaking the screen as per the other comments, but starting at the bottom and then going around the sides slowly worked for me.