Same thing happened to me, hit it with my head while installing the headunit.
Remove the plastic cover, you will see 3 bolts, remove them and a black plastic piece with metal in the middle will come off.
On the piece you probable have now in your hand, there`s a single bolt.
Yo are gonna have to unscrew that bolt in order to fit it through the metal part, once everything is a single part again, re attach the 3 bolts you took of and put the plastic cover back on
Hope it helps