If it is a hard epoxy resin, we have found two ways for removal. One is to use an old soldering iron and scrape away the resin, it crumbles once heated.
The best way we have found, is to use methylene chloride, an ingredient commonly used in paint remover. Build a dam up around the area to be removed, children's modeling clay can be used. Fill the area with paint remover, cover if possible as you don't want to breath the fumes. After a while, use a tool to scrape the resin free, it will turn to a rubbery-like material, it will peal off. Keep re-applying the chemical and repeat.
This technique was used to remove the potting compound from the old General Instrument Videocypher II modules.
Your potting compound could be silicon rubber, RTV, don't know how to remove it. However, one time I used RTV to seal a gasoline filler hose, after a while exposed to gasoline it turned to jelly. That was not our intent, but that might work too.
Any of these methods may also eat the color coding off of resistors, etc. Work very slowly.
Hope this helps - Jim