Depends how bad they are, kind of like sanding and buffing paint, wet sand scratches first, ( make sure you feather them out) don’t want grooves in the plastic, 1200 grit if that will do it, work your way up to 2500, 3000 if you have it.
Get the buffer out and start with a heavier grit compound on any tougher spots, get it as good as you can till switching to a polishing compound. (Polishing compound usually doesn’t take scratches out) Best to have a helper to hold on a blanket or something soft, I made a jig to hold it still while buffing and sanding, back side usually only needs a polish, but not always.