UA can check the bags through to BKK - just need to present printed itinerary for the ANA legs. Allow extra time to do so, since they need to do this manually.

UA will not be able to issue boarding passes for ANA flights. The passenger can use the connecting corridor and walk to Tom Bradley terminal and check-in at the gate, or exit security, take the interterminal bus to Bradley terminal, and check-in at the ANA desk. Make sure to present baggage tags so the check-in agent can enter the baggage tag information into their system.