The brass accelerator pump assembly will come out of the main body when you remove the top of the carburetor, assuming you didn’t disconnect the pump lever.
Brass doesn’t seem to mix well with cast iron and these pumps tend to get stuck when there is any corrosion going on. When the pump is stuck, apply heat to the outside. They will usually slide out. Worst case, drill a hole from the outside and using a drift punch drive it out. My guess is that if it’s this bad, the carburetor is toast. Tap the hole and add a screw or small bolt to plug the hole. Ethanol will eat any epoxy, so try not to use any epoxy, or adhesives.