Dixon
You can pull out some more of the insert to give you better screw access. If the screws were pulled out of the fiberglass cap and the holes are walloed, you can put in a plastic drywall screw molly or drill new holes either side of the original holes. If you are "re-using" the original holes in the rubrail, I would put the screws back in with a small SS washer to keep them from pulling through down the road if you take another shot. Finally, you can then tap the insert back in with a rubber mallet