Turn signal / corner light housings keep falling out

[Xyst]

Both front turn signal housings keep falling out while driving. They end up having by the bulb wire and klunking against the fenders.

How do I fix that from happening? I can slide the housings back in and the "click" in, but they keep falling out.

Thx!

 

[Xyst]

So I think I'm missing the retaining screw that goes through the fender into the screw tab. Anybody know what size and length screw I need for this?