Retroactively apply bills to PO

Retroactively apply bills to PO

Hello, 
We have some bills that have been created and paid within Zoho, but were not linked to the POs they were associated with (during a transition time). We now want to be able to accurately calculate profit per order, but can't because these expenses are not currently tied to their transaction. 

Is there a way I can retroactively apply these bills to their proper POs ?