One end of the clip is a hook, the other is a press on clip. On the clip end, get a knife blade, or a flat blade screwdriver under the lip and lift. if you can’t get to the lip, slide the knife blade under the clip, and lift on the clip end. In either case, put your other hand over it, so that when it pops off you don’t lose it or put your eye out.
they are made with a special rivet, which is pressed from both ends. If you have four piece snaps, you might be able to drill that rivet out, and replace it with the stud and post, if you have the proper setting tool.
easiest way, is to go to eBay or Amazon, search for windshield snap clip, and order a dozen of the proper size. They come in seven eights and three-quarter inch. Then you always have a handy replacement when you need one.