Help fixing ledge on board.

This is an odd situation. Kitchen counter ledge has absorbed some dog ear medicine from a bottle which leaked. It was painted but still absorbed and expanded, which makes me think it could be MDF. Don’t know. I’m assuming to repair I should start by sanding but then what’s the next best step? Guessing since it expanded I may need to fill in some imperfections with a resin or drywall sparkle. Would rather not try to replace the entire board as it would be a pain to do so. Thanks in...

Help fixing ledge on board.