Washing it with hot water and then scratching it off with a small shovel.
Scrubing it using rag with lacquer thinner (diluent).
Heating the film with electric hair drier and tearing it off. If there's any residue, you can use ethyl acetate to wipe it off.
Basically there is no solution. But you can try to use a heat gun. By the way, it needs patience.
