How to go from Terminal T2 to Terminal T3 at Beijing Airport?

I will arrive at Terminal T2 from Xi'an flight and I need to catch another flight at Terminal T3. I thought taking the express train but it seems that it goes from T3 to T2 but not from T2 to T3. Is there any other possibilities to make the transfert except to go from T2 then reach Sanyuanqiao station before to go back to T3? If this is the solution how long it takes to do that and do I have to purchase two tickets?
I thank you for your answer.