Hopefully they’re not landing in a terminal at all! It’s not good for the planes.

sonyeoshin is correct; most UA flights arrive at T7/T8, with international arrivals at TBIT only if they arrive when the T7 customs / border control is closed.

Getting from there to DL’s T2/T3 has only been possible for less than a year, and that’s going to be a long walk. There’s a landside all-terminal shuttle, but the loop around the terminals is one of the most traffic-clogged places I’ve ever seen outside of Asia. I’m honestly not sure which would be faster.