Looks like an ordinary pond snail.
As far as I know "pond snail" is an umbrella term for several species - I have no clue which this would be, but I think all pond snails are quite similar.
They are harmless - you can put it back in the tank, but you will never get rid of it ever again. They breed very fast and are utterly indestructible.
It's very common for them (or their eggs) to come with store-bought plants, animals or substrates.
Some people really hate them, because once they're established it's very hard to get them out. If you want a clean-looking, axolotl-only tank, keep the snail out and hope it was somehow they only one.
If you don't mind a few dozen snails minding their own business you can put her back and be friends with her. They eat algae and gunk, so I really like them.
If you have a lot of gunk and enough calcium for their shells, they can grow to decent sizes. The biggest I've ever seen was the size of a pinky nail, but that's very rare (at least for me). I have seen the axolotls eat the bigger ones once or twice. They generally ignore the snails since they're too small and slow to be spotted.
Technically, this could be a risk to the axolotl, because if they eat the snail they will also swallow the shell - if you have really bad luck this could lead to impaction.
EDIT: Ninja'd by Calgarycoppers. You're fast!