Rear driver side door will not open from the inside or the outside

Unfortunately, the only solution is the door panel needs to come off so you can try to manually move the latch. You are correct that this needs to be done from inside the door.

It will not be easy but on most all vehicles can be done with the door closed.

Take a look at the attachment and see what you can do with getting to panel off. Once it is off, you will need to spray the latch down with WD 40 and see if that loosens it up. If not, then you will need to pull the latch release with pliers if needed to get it to release.

Let me know if you have questions. Thanks