Being brutally honest? Take it back.
You don't have the room in a 50 gallon for a group and it wouldn't be fair to keep one on it's own, plus they can grow (if they're happy, which they won't be on it's own) to over a foot long.
There are many other ways to combat snail problems rather than adding fish and we don't normally recommend getting any fish to solve a problem.
However, if you have room and they're compatible with your other fish, you could think about zebra loach Botia striata. They do need to be kept in groups (all loaches are social) but are great snail eaters and grow to only about four inches, so are a much more sensible snail eater for a tank your size; I kept a group of seven in a 120l for many years.