There you have it. Slip the back back on, pry the edges back to where they were with the screwdriver or by pushing it on a hard surface. It may turn...
Here's an experience I, and most high school students go through at some point in their life. You wake up in the middle of the night, and remember that you need a padlock for P.E. the next day. You quickly rummage through all the junk in your room, and find about five of them, but you have no clue what the combination is for any of them. You look on the Master Lock website, and there's a two-month process you can go through to get the combination. You look on youtube and all you can find is a guy with a weird equation that only narrows it down to 100 combinations, which could still take up hours of your time. This instructable will show you how to find the combination to a master lock. **Notice! This is only to be used in an emergency where you need to open the lock. You should never use it to break into someone else's gym locker. Besides, there's nothing in there but smelly, sweaty gym clothes, and maybe a stick of deodorant.
Find the newest looking padlock you have. This will work with most master locks, but probably not the really old ones. You will need a padlock and a FLATHEAD screwdriver.
Turn the lock so the back side is facing up. Pry up the edges around the back using the screwdriver. It is only important for you to pry up the bottom half of the circle of edges.
Once you have at least the bottom half of the edge circle pried up, you should be able to slide the back panel off, so it looks like it does in the picture.
There should be a circular hole like in the middle of the picture where you can see the edge of a circular metal disk. If your lock by chance does not have one, you can try another lock that might, or attempt to drill a hole.