Incheon International Airport's official Terminal 2 to Terminal 1 international transfer guide says: from your T2 arrival gate, follow the green Transfer signs to the B1 shuttle train platform. Take the Concourse-bound shuttle train, change at the Concourse to the Terminal 1-bound shuttle, and arrive at T1. The airport lists 5-minute service intervals for both legs and warns that you cannot turn back after boarding. At T1 go through transfer security screening on Level 2, then proceed to departures on Level 3. If you do not have a boarding pass, check with your airline; transfer desks are listed on Level 2 before security and Level 4 after security. This is an airside international transfer route, not instructions for a landside terminal shuttle bus. Confirm eligibility and timing with your airline.