Problem with Jeep Grand Cherokee 1994's back passenger door that will not open?

I have this vehicle and got it with the back left side passenger door shut and cannot be opened. The locking button slides back and forth but feels loose and has no effect to help "unlock" the door. I have a feeling that something inside is the problem,but to remove the door panel to check that would the door not have to be open?
Is this a Catch-22?
Help!
 
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