Where do I go in Beijing International airport

You do not need to change the terminal and both of the two airlines are in T3.
The procedure is like this: Arrive at the International Arrival Level at 3F of T3-E → proceed with transfer procedures → pass through the Transit Inspection in special passage in the east or west → take special elevator downstairs to International Departure Level at 2F of T3-E → accept Security Inspection in the special passage → go through the customs sample check of hand baggage if necessary → Waiting & Boarding