Loose headlight

I have a 2000 fleetwood tioga class C ford e-450 triton V-10
And one of the headlight is loose and will not seat into the chassis
I have tried looking online to find a website on how to repair/replace the entire headlight but no luck. It looks like a peg type fitting seats the lamp into the chassis but mine keeps popping out and becomes loose
Can someone help me out or assist me in the right direction