First thing I would do is check for codes and see if anything comes up. You may not be able to get it with a generic scanner unless it's one of the P codesm so this may not be something you can catch with a generic reader :/. Worth a try if you have one, but unless you have a scanner that can read OEM codes, you're potentially not going to have much luck.
That being said, the first thing I would try is a new OEM fan (even if you buy it used) to make sure it is not a compatibility issue with Hyundai - Hyundais tolerate some aftermarket parts better than others, but engine bay components tend to be a crapshoot with some of them. The days of cars tolerating aftermarket parts in the engine bay (and emissions) well is long over, especially with Amazon garbage. You can also check the fan circuit as well, but it could require a bidirectional scanner, which isn't going to be cheap by any stretch. The OEM fan will probably be cheaper than a bi scanner :/. Something like this might work, but it's not bidirectional: https://www.amazon.com/dp/B0B8H2C4WH
This scanner is bidirectional and similar to the Xtool on base price, but I have seen the Xtool for mid $200 with coupons a lot more often:
https://www.amazon.com/Bidirectional-Thi...
https://a.co/d/5mzXtlt FCA AutoAuth support
https://a.co/d/3i24Uz9
It's rare for the relays to fail, but it's not impossible - I would see if you can get them out and test them with a multimeter. You can use a $50 4,000 count Klein TRMS for this if you want, you don't need a $100+ Fluke or 6000 count TRMS meter.
As long as you did not disassemble the cooling system and remove lines, it is probably not due to air in the lines. If you did, you may need to bleed it. You may want to try bleeding it given you did change the thermostat, but for the most part any respectable all system scanner can do this at least. They're not cheap at $300+ so if you can lift the car and let it run for a bit with the radiator cap off, that will be the free way to do it BUT it could take longer.
crwdns2934105:0crwdne2934105:0
crwdns2934113:0crwdne2934113:0
crwdns2915270:0crwdne2915270:0
crwdns2889612:0crwdne2889612:0
2
352 
284 
155 