The 2012 kia optima offers the remote start feature on select models, such as the sxand ex models. this will come in the form of a key fob. if the fob is not working then you need to check the battery. all key fobs use the same type of battery, which is a cr2032 battery. these are small coin-shaped batteries and they will cost you about 5 dollars each on average. you can find them in the same place you would normal batteries. to change the battery you will need to remove the back panel of the fob. some fobs are different than others. you may be able to simply pull down on the back and have the piece slide off. if so then you can simply remove the old battery and put the new one in its place. however, you may need to remove a couple of tiny screws before you can do this. they are not hard to get out, as long as you have a small enough screwdriver on hand.
The 2012 kia optima offers the remote start feature on select models. remote start is an available feature on ex and sx models.