Screen replacement ways to teardown without heat gun

hairdryer works as well as a hot air gun or these guys sell a microwavable sack thing that you microwave and is designed for resting on the screen to melt the glue i think its called an iopener, but really you just need some heat to soften the glue a hot water bottle would work just as well as long as you make sure its dry

Any gentle, non-focused heat source should be fine. A hairdryer, space heater or radiator will all work. Just be careful to not get it TOO hot, otherwise you could damage the motherboard or LCD.

I personally use a gel hot/cold pack from the drug store. Microwave the pack then place on back of phone for a couple minutes and the back comes off in one go.