Water leak from the wall above the entrance

[alessandrocube]

Hello everybody!

3 days ago when we took our GC 680 from the VW service we realized that the piece above the entrance was slightly detached and we pushed it back in its place. It keeps detaching when driving on bumpy roads. Today there was a heavy rain and we realized there was some leaking from it.
I would like to know what that piece is covering and what its purpose is. Also, how could I fix it?

I attached a picture where I'm showing the piece I'm talking about!