Chemicals will damage the steel plate! 1. Scrubing the door using hot water with washing powder. 2. I don' t know what metarial the surface of the door is made from. Thus I don't know the film can be cleaned by knife. 3. Using chemical reagent: lacquer thinner which is sold everywhere. By the way, you can heat the film with lighter to make its edge curl, which will make it easy to tear the film off. It won't damage the steel plate.
