You have to push upwards on the cup (or lanyard loop) to get the hole in the frame and slot in the cup to line up. I put a small round headed screw in a small block of wood to set the bottom of the cup on for the guns with no lanyard loop. It it has a lanyard loop you just need a flast surface to push the frame downwards again.
Good luck with it. Oh, you shouldn't really have "drive" it in with a punch and hammer. Once it's aligned it should push in. You might need to use something to push on the end of the pin with to protect your finger tip.
