This happens quite often: after inserting the rivet in the previously drilled hole, the rivet mandrel gets stuck in the tips. Then, since you cannot continue the application, this slows down your work. Anyone who has been involved in this situation knows that it does no good to try to pull the workpiece out with your fingers or another pair of pliers. It just doesn't work.
The desperation is so great that you think about opening the whole tool or even buying a new one. Before you get to that point, there is a practical way to remove the part without damaging the tool. Leave the rivet crank loose and partially place a new rivet in the locked point. Then, give it a "hammer".