If you have big fingers like me, i found that to make it easier, i cut a lead off of an LED (or pin , etc) , heat it up with soldering iron, and push it into the black plastic VERY CAREFULLY not to touch the lens. Then trim it so you have a little rod to actually grab onto. You can use those push pins with the plastic round head if you want to make it even nicer.
I cut a hole in a black plastic piece that happened to be the right size. Then I fit it to the top edge of the threaded optic housing. I just wish I had better optics.