I had that problem with a rear door on my 91 sedan. I opened the other rear door, removed that inside panel, and had a look at the latch mechanism & actuators. Then...I was able to make up a tool with a hook (bent coat hanger) that I got down inside the non-opening door with the glass lowered, and pulled the lever up that should have been worked by the inside handle. The plastic 'keeper' had broken. I got a replacement from one of the HELP bubble packs at an O'Reilly's Auto Parts. While I was at it I unbolted the latch and made sure it & the other parts were all lubed before I put things back together.
Also, on my 92 Escort wagon, the driver's side rear door handle -the outer handle- had siezed from rust or whatever. I had to remove it and soak it with penetrating oil, and lube it too.
I also oil the door hinges a couple of times a year.