Help Needed.

Looks to me via them pictures that the lense must come off in order to fasten black plastic part to wherever, maybe it has small tabs holding it in place go -on be a bit rough with it

 

That’s good David. I use these on my trailer as side lights and as night lights on the boat.
Can be quite sticky, but I suppose that it part of the fitting.

 

Good man its amazing what a good old screwdriver attack will solve.