Cindy;
Turn the water off to the toilet at the UDC. The front plastic cover on the toilet is held on by velcro. Just pull it off. Then you will see a large hose clamp holding the top half of the toilet on to the base. If you have the side cover off already, you can see how to disconnect the water inlet line from the ball valve. Then take the top half of the toilet off and you can see how the stopper ball is connected. It sounds like the screw that secures that mechanism has come loose. It's not a hard repair. When you put it back together, make sure the toilet is centered on the large rubber seal. When you open the stopper ball, the seal should appear equal all around the opening.
Good Luck
John