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Be careful while doing this step, because overheating the stain can make it worse. The trick is to make the mess malleable because it won't budge while it is hardened. If the mess is in the oven, preheat the oven at the very lowest heat setting. Stay by the oven to make sure the stain doesn't overheat and start smoking. If the stain is on another hard surface like a table or wood floor, try using a hair dryer to warm the substance. The plastic or wax should have softened with the heat, and you can begin scraping it off with a flat, sharp edge. This will require some elbow grease, but be careful not to scratch or chip the surface you are cleaning. If you do not have a putty knife, you can use a butter knife or a razor blade. If there isn't much of a mess left, this can be achieved with mild soap and a damp rag. In the case of more persistent stains, you may want to use a more heavy-duty surface cleaner and a rough sponge or scrubber.
Heat up the plastic or wax. Chip away at the substance with a putty knife or something similar. Clean up the area where the plastic or wax had been.