If your screen is badly cracked, covering it with a layer of clear packing tape may allow the suction cup to adhere. Alternatively, very strong tape may be used instead of the suction cup. If all else fails, you can superglue the suction cup to the broken screen.

Depending on the age of your phone, this may be difficult. If you are having trouble creating a gap for the opening pick, apply more heat to the edge and try again. You may need to repeat this step multiple times.