Depends on where it is leaking. If it is leaking at the pan gasket, then try tightening the bolts to 20 lb/ft torque. If that doesn't work the gasket will need replacing. This is a good time to have the fluid and filter changed. If it is leaking at the seals then you can try a can of some sort of transmission stop leak. Any Auto Parts store can recommend one. May or may not stop the leak. If the leak persists and is more than a few drops a day, the transmission will need repair by a pro.