The easiest way to get the low tire pressure light on the 2015 kia optima to reset, is to inflate all the tires to the pressure listed on the vehicle placard, which should be on the door jamb of the driver's side. sometimes you need to inflate a little bit over that amount to get it recognized, and then release the pressure later to the proper amount. if that fails, try turning the ignition to the on position without turning the engine itself on (after parking and setting the parking brake!). then, hold down the pressure warning reset switch, which you just find located just under the steering wheel, until you see the tpms light blink three times. this should reset the light, but it may take the ecu a couple minutes to fully acknowledge it.
To reset the low tire pressure sensor on the 2015 kia optima you will hold down the pressure warning reset switch which is located under the steering wheel until you see the light blink three times.