Replace a catalytic converter

What is the reason you're replacing the cats? I ask because they can cost $1-2k on average new. This isn't something you replace first, usually someone stole them or the cats broke inside. Get the car scanned by a parts store or by a mechanic (though a mechanic will probably charge you but the report will be more complete).

That said, a lot of cars these days integrate it to the rear exhaust assembly at the end and you buy it as a integrated part of the exhuat system. Some cars still split them off, but "compact" models usually necessitate a rear exhaust assembly to replace it. Apparently it's a known issue on your car when I did the research to see what they cost and how it's done: https://www.kiasoulforums.com/threads/th.... There is a possible recall, so take this to Kia if the cat is indeed bad before purchasing one.

Check your VIN on this site: https://owners.kia.com/us/en/recalls.htm...

That said, you have two paths you can take: If you're in a non inspection state, do nothing - really. Don't cut them off and break federal law, but your CEL will be on permanently. At least where I am once our cars get the drededed P0420 (or family of codes, like header cat failure), we don't fix crap on our cars when they're old and high mileage, until they impact performance (and 8/10 times, something else failed before a 94% efficient cat that FUBARed the car so it's junk). That said, something else expensive usually goes before the cats here so you can probably get away with it -- this is also why I would never buy a used cat in my state - we all ignore it so you're probably getting bad cats here.

If you are in an inspection state, you sadly need to fix it or sell the car to someone in a state that will fix it, or simply ignore the issue (as in Florida, where the cat can be 94% or worse and as long as it's not doing anything, we don't care). This is a part costing over $ 2,200 for this car :-(. Not a cheap issue. The P/N is 28600-B2500 for the intermediate pipe which integrates the cat to it.