Unusual mountings on the plate holder

Hello together, I wanted to change the license plate holder at my car today. So corresponding license plate numbers out, (4) screws screwed out of the holder and then tried to remove the holder. The latter did not work, because the license plate holder was still held at 4 points by strange plastic clips. These clips can be found both at the front and back of the license plate holder and sit bomb-proof. I don’t have the slightest idea what these holders are and before a Google and Youtube didn’t help me, because I couldn’t find anything where someone had a similar attachment. Also a buddy who works in a workshop was baffled. It’s round plastic clips with round recess in the middle and it looks like there’s a screw in the middle that was cut off. It’s hard to explain, I hope the pictures bring it over well. Has anyone ever seen something like that and if you can’t explain it, it’s not easy. yes, what is the correct way to solve this?