this is a well known weakness of pro mice. i really doubt you'll have luck opening and closing it-- probably just better to buy a new one. But if you go that route, you might as well try to open it, for curiosity's sake..
if it were me, i'd get a very tiny flat screwdriver and just start gently prying things up, until it becomes clear how it's held together. a magnifying glass can help. but there's always the chance that it's sealed shut--
pnw