There's 40 some different pins, you do not want to lose any if you can help it as it helps the rigidity of your keyboard.

Put the pins back you will want a thin small tool that you can push the pins back in. Be careful sometimes putting a pin in can pop another out.

It's a good idea to have a magnet on the side too, so that you can test the pins and ensure they're in properly. Check a lot since mine seemed tight but as I put pins in it became loose.