Not sure if it actually tightens anything, but if you (gently) pull off the cover on the underside, there are 4 screws that you undo to take it apart...you will need an allen key to remove or tighten these.
If you are taking apart be careful...it can be a little tricky to get back together. The cover easily snaps back on again.
However if your car is under warranty I would take it to the local stealer if you can afford the time.
