How to enter credit for Freight against a previuosly invoiced PO?

Hello,

I apologize if this post is a duplicate, I was unable to locate my original post, so resubmitting here.

We would like to know how to enter a Credit for Freight Charges against a PO that was previously invoiced for Items plus Freight.

We would like to be able to enter the Freight Credit so that Payables will automatically split and distribute the credit proportionally against the Item lines and distributions on the PO and Invoice, the same way the original Freight charge had done.

However, Payables does not seem to allow us to match the Freight Credit to the PO, nor allow us to enter it as a correction and point to the orginal invoice and Freight charge.