How do we handle RMA between internal entities.

Say we have two organizations A and B where A sources from B and Customer C orders from A. Flow between A and B is using IR/ISO. When Customer has a RMA back to A, and the servicing/repair cannot be done in A, then how does A send it to B. Again IR/ISO? How to link it to the RMA? Any suggestions? Also to make things worse, there is a transfer pricing.