Heat an iOpener and apply it to the left edge of the screen for one minute to help soften the adhesive securing the screen.

A hair dryer, heat gun, or hot plate may also be used.

If your display 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.