How to define Average Cost for Item in Inventory Org

Summary:

we have an item for which perpetual average cost is already defined for Cost Org - Inv A and Cost Org - Inv B.

User is trying to create transfer order from Inv C to Inv B and getting transfer price issue. While checking Item unit cost is defined during the time of on hand load.

Now the Item has on-hand quantity of 2000 and Inbound quantity of 1000 against Inv C.

My question is how to define perpetual Average Cost for Inv C in system. And flow of steps which needs to be performed to correct the issue. If there are any miscellaneous transaction needs to be done.