Are you on separate tickets or one ticket? If separate, the gate agent in Atlanta doesn't have to check your bag all the way through but some agents may, especially since they are partner airlines. If your bag is checked through to Bali then you do not clear immigration or customs in ICN. You stay in transit and your bag will be transferred. If your bag isn't checked through then you do need to clear immigration in ICN, retrieve you bag, and recheck it in with Korean. I will say 90 minutes is very tight for the latter.