How do I get melted (and now hardened) plastic off of fabric?

Here is one remedy that at least makes sense to me. I have not personally tried it, but I know melting the plastic again seems like it will be part of the process.

Very carefully….?

Have you tried putting it in the freezer?

If it’s a polyester fabric, then the melting plastic may have fused to the fabric and it may be impossible to simply remove the new material.

Offhand, though, I sort of like @cheebdragon‘s approach to freezing it to see if the contraction that will occur then may be enough to break the bond (or maybe just get it brittle enough so that you can simply hit it with a rolling pin or something to break it off).