If the 2013 kia optima steering wheel controls are not working then the fuse is bad. to get to the fuse box look to the left of the steering wheel look for a small seam or crack along the dash. using a screwdriver or prybar you will want to pop this open. on the inside, you will find a bunch of fuses. on the back of the panel that you pulled open, you will see a diagram that will show you what each of the fuses is for. if this is not on the back of the panel then you can also find it in the owner's annual for the vehicle. once you have figured out which fuse you need simply pull it out. the two sections that stick up should be connected by a thin strip of metal. if this has been broken then the fuse is no good and will need to be replaced. if this strip is there then the fuse is fine and can be popped back in. new fuses will cost you about 10 dollars, so they are pretty cheap.
The most likely cause of your 2013 kia optima steering wheel controls malfunctioning is a bad clock spring or control module.