Apply a suction cup to the heated bottom edge of the back cover.

Make sure you did not mistake the screen side for the back cover side.

If your back cover is badly cracked, covering it with a layer of clear packing tape may allow the suction cup to adhere.

Lift on the suction cup with strong, steady force to create a gap.

Depending on how aged your phone is, this may take significant force. If you are having trouble, apply more heat and try again.

Insert an opening pick into the gap.

Don't use metal tools to pry, or you'll mar or shatter the glass back cover. If the panel won't budge, apply more heat, either with a hair dryer or heat gun.