How can you fix a misfire on cylinder 2 in a 2004 Kia Optima EX 4 cylinder?

I would start with replacing the spark plugs. Should be around $20 for the set. Disconnect the battery to re-set the check engine light. If that doesn't take care of your problem and you get the light again, go to Autozone and get the coil that mounts on the #2 cylinder plug. You have two coils, on #2 and #4. Cylinder #1 jumpers to #4 and #2 and #3 are jumpered together. It is real easy, just disconnect the molded plug that runs to the coil, remove two bolts and remove the plug wire that goes to #3 cylinder. Hope that this helps.