if the ding in your epoxy board goes all the way to the foam you cant use anything but epoxy cause if you put solar resin or sun cure or regular fiberglass resin it will melt the the foam and you'll have a bigger hole than you started with but if its just a crack rough it up with some hundred grid than glass it with sanding resin than sand it again until its flat than reapply another light coat of sanding resin
and than sand it with 200/150 grid until its smooth
than if you want match the color you want spray a light acrylic color than spray some clear coat and sand it with wet sand paper like 1500 grid if you do it right you cant feel or even see it