I would be VERY careful when messing with eye caps. If it is only one stuck eye cap, I wouldn't even attempt to remove it. Just increase the humidity for the next shed cycle and it should come off on its own.
Their eyes are just so fragile it isn't worth messing with if its only one stuck eye cap.
We just had a story here recently of a vet attempting to remove some stuck eye caps and actually removed the protective layer over the eye. The snake is going to loose one of its eyes and possibly the other.