The H clips are easily damaged if you are not careful but you can get spares from Rimmer Bros..
Gently press down adjacent to the pin, on the clip nearest you with a small screwdriver and hold it down. Then push the pin through the hole and away from you using a suitable drift or whatever you have to hand, that is a slightly smaller diameter than the pin. Once the head of the pin has gone past the H clip, now press down and hold down the opposite clip and push the pin out through the back.
