Any old plastic polish should work. There's one called PlastX that's good, or there's a product specifically made for coin slabs called Slab Renew.
Well the coin is clearly a 55-D/S and luster and surfaces look pretty good with a rather weak strike. It surprises me that this coin didn't get MS66 and there are too many major marks for MS67. I'm guessing MS65, but I still think it belongs in an MS66 holder.