So I have a 2018 Kia optima FE. I recently noticed that I have moisture in the right headlight. How should I go about fixing this? Is it covered by the 100,000 mile warranty on Kia? It has been there for a few days.
I'd also check and make sure that not only are your access covers on, but that the vent plate is still attached. It's usually a piece of dense foam stuck on the bottom of the headlamp assembly, to help regulate internal headlamp pressure, and keep moisture down. If you don't have a vent plate, the vent tubes should be checked to make sure they still have their C-ducts still attached.
The simplest solution however, is to switch to LED lamps, as these will eliminate much of the heat that can cause condensating, as well as circulate air withing the headlamp assembly with their built-in fans, which will also keep condensating down.