I will be due for the second regular service, but it is not that convenient for me to use the dealership. Can going to midas or other reputable auto service instead cause any warranty problems? TIA!
I have never found Midas to be a good place for service, and I wonder if they are generally considered "reputable". There might be some Midas shops that have good general mechanics, but there are a lot that seem to have people who have been trained in installing exhaust parts, but anything else that you let them do is probably a mistake (based on my limited experience).
Sometimes I work on my own car, sometimes I take it to the corner garage that has people I have learned to trust for certain kinds of things, and sometimes I take it to the dealer.
Years ago, I purchased a used Honda Accord: it was about five years old but in really good shape. After a few months, I took it to the local Jiffy Lube for an oil change. They over tightened the drain plug and stripped the threads, which left a big puddle of oil on the floor in my (rented) garage, and then when I brought it back to them and complained, they responded by putting in an oversize plug, rather than fixing it properly by replacing the oil pan (about a $30 part, but it would have required pulling the engine out to replace it, so their reluctance to repair it properly was somewhat understandable). And the funny thing about that whole experience was that the dealer was matching their price for oil changes - would have been less convenient, but wouldn't have cost any more if I had gone to the dealer, and I could have avoided driving around for the next five years with my heart in my mouth every time I went in for an oil change, wondering if this would be the time that the hack repair job gave out and I would have to spring for the cost of changing out the oil pan.
To answer your question, you should be able to have your oil changed anywhere and satisfy warranty requirements, but you do want to ensure that they use the oil specified by the owners manual (which is more expensive than average), and you would do well to keep documentation of the mileage and the type of oil that was used, in case you do have a reason to ask for warranty service in the future. If you're needing other kinds of service, it might be a mistake to take it to anyone but the dealer, depending on what needs to be done. Most places should be able to rotate your tires, replace air filters, etc. But something like changing your clutch fluid seems to require special equipment that only Kia and maybe Hyundai dealers are likely to have.