Lay the iOpener clear-side down, flat on the edge of the device, over an adhesive seal you wish to heat. The liquid will flatten the iOpener against the surface, ensuring good heat conduction.
Let the bag sit on the device for approximately 90 seconds before attempting to open the front panel.
At this point you should be able to begin prying under the screen with a plastic opening tool. Be sure to see your device's specific guide for where and how to do this.