Don't you mean left?

Just make sure the traveler exits to the left, following the sign for CONNECTING FLIGHTS when s/he arrives. Anybody can exit through that door, and it is actually more convenient if you're taking BART.

Meanwhile, make sure you are in the area of the baggage recheck and transfer desk on the lower level. (It should be fairly obvious. There's a bank of payphones right in that area as well.) There is a large door where passengers will be exiting. That's the door I think we're talking about.