Kia Maintenance Questions? Ask a Mechanic for Answers ASAP
From what you say the door is shut and the panel is still on it. These Optimas have a problem with latches (the part that holds the door shut) and it needs to be replaced. The release lever tends to go next to the lock pawl rather than stay on top of it causing the latch to stay locked.
Carefully pull the top of the door panel up over the top lip and toward the inside of the car.
Take a long screw driver or what ever and try prying the plastic piece off of the latch inside the door. You can retrieve it when the door opens and a new latch will come with one.
Once plastic is off. In the middle of all these levers and rods you should see a square looking metal piece. With a long screwdriver, rod or dowel (something stiff) push down on this and the door should unlatch. If not try pushing,pulling on all levers while working the lock button and door handles. This is very hard to try and explain being online. Push, pull, wiggle and wobble until you hit the right combo. If all this fails, someone handy with a slim jim may help.
Let me know how you make out. 95% sure latch is faulty.
Good luck. Keep at it with the plastic off you will succeed.