Accidentally dropped my phone right on the back.
With a heat gun on low the glue softened up very easily. Needed something sharper and thinner to get under the glass but once I did it peeled off easily. Removed all the old glue with a knife to hopefully retail some water resistance.
Use the heatgun until your phone is uncomfortably hot around the edges. Then use something sturdy and thin to get under the glass or the suction cup if you can, once you have enough space stick an opening pick in the space and go around the edge and be careful because there tends to be more glue further in the device.