I used a hand towel folded in half and a clothes iron on the cotton setting (med-high heat, no steam). Placing the doubled towel between the phone and the iron, I would set the iron down for about 20 seconds (my iron has a timer that beeps when left horizontal for too long). Lift the iron, check the temperature (aiming for just too hot to touch), reposition as needed, repeat. It took me a while, but that’s because I took my time not knowing how fast this would heat. All-in-all, about 2 minutes to reach the right temperature to loosen the adhesive (it IS tenacious).