Check the condition of the wiring harness in the affected tail light. This may either be a deep electrical issue or the harness for that tail light is bad. If it looks good and you want to try something, pry the positive connection up a few inches with a knife if you're having issues with poor connections blowing the bulbs.
If you keep having issues with the bulbs, replace the harness; [https://www.kiapartsnow.com/|Kia Parts Now] sells the harness. Put your VIN in and find it that way to make sure you get the right harness.