Are you talking about the Top Firebutton Super?
If so, you need to remove the fire button switch, and the assembly that pushes on it--which it sounds like you did.
(Pay close attention to how it is put together, so you can get it BACK together when you need to).
Once that's out of the way, you need to pull on the bottom cap that presses the lever for the fire button off of the inner shaft.
If you look at the exploded view at Happs, it's a press fit onto the inner shaft.
You will probably feel like you're going to break it before it comes free.
A little twisting may help, but don't twist too much because the inner shaft is a piece of plastic.
The first time I disassembled mine, I finally hit the "if it breaks I'll buy another one" stage of frustration before it came free.
After you get it free the first time it's usually pretty easy because you won't put it back on as tightly as they did at the factory.