A friend of mine picked this up a few months ago at an estate sale and wanted to know if it can be restored and still get a good grade if he has PCGS restored and recapsulate it with a grade. Sorry about the duplicate photos.
It's only about 35% silver, the rest nickel and manganese. There were 120 million minted, so don't put much effort into "reshining" it. As above acetone or some silver cleaner to dip it, and you shouldn't even think about certifying it or having someone clean it for you. The cost to have anyone else clean it up would/will be over 10 times what to coin will ever be worth. Just keep it as an oddity.
The cost to conserve will outweigh the value of the coin many times over. You can try a little acetone, not mail polish remover, but pure acetone.