Sorry it took so long to follow-up on this. I recently flew in to ATL from ICN for my connection to CLT. As soon as I went through customs and picked up my baggage to check back in for CLT flight, I stopped at the Delta desk right there before the exit (left for connections, right to go exit to Atlanta). They confirmed that once I get through customs, I just go to them there and pay the pet fees for my flight to CLT - simple as that. Thanks for all the responses!