Sure you don't push it in instead of pull it out? On many, if not most, sterndrives and outboards with single-lever controls, that's how they operate.
If not, see if you can get the little flat head
screw at the base of the lever out, and see if that lets you unscrew the lever. Once you get the lever out, that should let you remove the exterior bezel and perhaps either free up the knob or give you acess to remove the complete control and clean it up off the bulkhead.