Light Falls Out

I have a 20X40 IG liner pool that was installed two years ago. Since day one the pool light (500Watt) has not been mounted in the nich (Just pushed in) and floats out once in a while. Installer keeps indicating he will fix it but after two years I am giving up on him and going to try and fix it myself. I am not sure but I think it is a pentair light. Does anyone know how this light is supposed to be mounted in the niche ? (Diagram)

Thanks

I believe there is a small hook in the 6 o'clock position of the light that hooks over a lip in the bottom of the niche ring. There is then ONE brass screw at the top of the light that screws into a threaded tab in the niche at the twelve o'clock position. That screw may not be quite long enough to take a "bite" into the threads in the niche. I had that issue. :)