Removing scratches from a dashboard can be difficult because of the way in which dashboards are formed and painted. A dashboard is typically moulded plastic. It's heated, formed and then allowed to cool. In order to fix a scratch, you will need to either fill the hole or gently polish the scratch, depending on the size.
Mix the epoxy according to the manufacturer's instructions. It may be helpful to add paint to the epoxy in a shade that matches your dash's colour as closely as possible.
Using the supplied applicator, apply the epoxy to the scratch. You are attempting to fill in any gashes in the plastic. Allow the epoxy to dry.
Wet the sandpaper and very gently smooth out the rough edges of the epoxy. Sand in one direction. Do not use circular motions. Try to keep your sanding to the epoxy area only.
Wipe the surface down thoroughly with the Mr. Clean Magic Eraser. This will help to smooth out any imperfections in the plastic.