Side door was slammed shut hard and now door wont' open
There must be a way to get the inside panel off. Then you could see and work the handle levers. From the handles to the latching mechanism, small rods work them. They attach on both ends. You will be able to see how the handles trip the latch, then grab the right rod and pull or push it in the right direction to open the door latch. You can do it, hard to describe w/o seeing one, but all work similar. Little rods, that's all you need to know. Uh, well, getting the door panel off is the biggest hurdle. Several screws, some may be hidden, be patient, plastic pin type fasteners along the bottom and up the sides of panel have to be popped out-usually one about every 4-6 inches. Once you get it loosened up, you will easily find the rest of the attaching points. Lift the panel up from the window channel and away. Peel the plastic ("waterproof barrier") film off carefully. You will want it to get a good reseal when you are done. Now you can see the inner parts, and how the handles operate the latch.
Once opened, spray with a penetrant, check the door sill all around, check for visible reasons it stopped opening. Sometimes the rods get stretched or bent, and the handles won't work. Good luck, big "do not slam" sign on that door, okay?