I am by no means an expert but I don't think you can do much with that. Not really many cleaners than can dissolve that and preserve the PCB. You could try isopropyl alcohol but I doubt it'd be enough.

I wouldn't have any problem with carefully picking or gently scraping away the epoxy over the wires until you get to the board. Your real challenge will be removing and then re-soldering the wires. It can be done with patience and the right tools.

I would just remove the epoxy. The board looks like it was dipped in humiseal, which might be more difficult to remove than the epoxy.

when you remove epoxy be very careful around the surface mount components, you can potentially break them if you aren't cautious.

sand down the epoxy

I would leave the wires as is, then splice solder them back together with some heat shrink tubing over the cut wires.

Good chance that is silver solder on the panel board... PIA to work with...