Replacing 1994 license plate light?

I know this is probably a stupid question, but one of these lights is out, and I have to replace it to get my car to pass inspection. I can't find my Haynes manual.

I've figured out that the fasteners that hold the fixture in place aren't screws, but just pop into place. (Great idea--make fasteners that just look like screws.) However, I can't seen to get either of them out with a screwdriver, and I've already used as much force as I think I can without breaking them.

Is there some trick to getting these out so I can replace the bulb. I've tried to do it from behind, but it doesn't seem possible.

Thanks!

OK, so I found the Haynes manual and the original owner's manual. Neither says a single thing about how to replace this license plate light. I took the taillight assembly off, but that still didn't give me access to the lamp.

Any help is greatly appreciated. In the state where I live, I have to pass inspection before I can pay my annual registration, so this one thing is holding up the whole process.

And I called a local Buick dealership's service department. They said they knew how to do it but wouldn't tell me how--they'd only do it if I paid them.

For anyone trying to do this in the future, it took me a while to notice that the center of the black plastic "screw" was separate from the outer rim around it. You have to pry to center piece out with a screwdriver. At that point, the fixture will come out.