At ATL, most of the baggage re-check counters immediately after Customs belong to Delta, which is unsurprising given the preponderance of DL flights there. IIRC, immediately after that you go through security and beyond that you can find your way to the train to the other concourses. The train is pretty efficient, if utterly soulless in the way that most US airports seem to be. The concourse where the international flights arrive is probably the least unpleasant of all of them, so if you have lots of time you might want to think about finding somewhere to wait there rather than in your concourse of departure.
Tip - Make sure you repeatedly check the gate that your onward flight is departing from. They can change. In an airport the size of ATL, you don't want an unwelcome surprise very close to your departure time.