Switch off your phone.

Heat an iOpener and apply it to the back of the phone for around two minutes. This will help soften the adhesive securing the rear glass.

You might need to reheat and reapply the iOpener several times during the rear glass removal.

A hair dryer, heat gun, or hot plate may also be used, but be careful not to overheat the phone—the display and internal battery are both susceptible to heat damage.