If the screw is just spinning in the body, put a drop of super glue on the tip of your
allen key and let it dry. Once it is dry, you can twist and pull the screw at the same time. If the hole is what is stripped out, and you have some mechanical aptitude, switch it to a 3mm or "M3" button head screw. You will have to drill a clearance hole in the eye cover just big enough for the screw to pass ...