How to reverse a purchase order linked with transfer orders?

Hi Professionals!


I purchased 30 items to the Blue warehouse through a purchase order. And then I transferred these 30 items to Red warehouse using a transfer order.

Then I noticed I needed to reverse the purchase order with a credit memo. And in order to make my purchase receipt line in the Item Ledger Entries open again, I transferred back the 30 items from Red to Blue. However, I still could not make the initial purchase receipt line open. 

When I tried to modify the applications with Application Worksheet, it told me "Entries applied to an outbound transfer cannot be unapplied".

How can I make my purchase receipt line open again and create a credit memo on it?

Thank you!