When I used to tint, it was the worst fucking job to do. Its called sweating. you cut a large peice of plastic enough to cover the rear window, or use a peice of blank backing (window film pull) the size of a back window that we just did that day. It would work so much better to leave the car out on a hot ass day and bake the hell out of it. Spray the hell out of the back window with ammonia and keep going back out there throughout the day, and keep spraying ammonia on it then start peeling what you can, and whatever is left, we would use a green 3m scouring pad. I will say that this is a lengthy process. But it is the most assured way to remove the film and to save the rear defroster grid.

They were the shittiest jobs and we would have the newby tint installers do tint stripping gigs, and the fucked up thing is the installer would get paid for the incentive of the new tint and the stripping.