Wow, that's the BB gun version of a bolt over ride. Put the two receiver halves together and pop the pins back in. Since it's a BB gun bolt carrier, I wouldn't take a hammer straight to the bolt carrier, so try cutting a piece of dowel and hammering it forward. If theres a round wedged to the side of the bolt, above the bolt, above the bolt carrier, etc, get a knife, leatherman, or whatever to pry/cut/destroy/remove the obstruction by force. Then proceed to drive the BCG forward so the bolt's back in the chamber. That way you'll be able to separate the lower from the upper receiver.
If yo