How can I fix a jammed lock that won't allow the door to open.

You would need to remove the door panel to get at it, which is not easy considering the dor is closed. You might have to for the panel off. If it is a dislodged linkages, you should be able to open the door by fixing the linkages. If the latch is bad, that would be tricky. You would need to break part of the latch to get the locking mechanism to release the latch.