Trying to remove the clock adjustment button on the glass

I'm doing a quartz replacement in the clock on my '77 280. I already have everything set to go, but I need to remove the button on the glass of the clock bezel that adjusts the time. I can't see how it's assembled together, and after experimenting with a parts clock I had, I broke the glass / plastic, whatever it is. So before I change the real one, I'd like to figure out how to safely remove it without breaking the glass. I'm going to keep messing with it, but figured I'd check if anyone had any experience with this. Thanks