Currency Code issue in Purchase Order

I have created a purchase order and warehouse received goods. Unfortunately forgot to give currency code USD in PO. Its not allowing to change PO currency code after Warehouse Good Receiving. Any idea to change currency code?

Go to the PO

click oder Button-> click receipts , posted purchase receipt list form will appear.

click receipt button ->click card ,posted purchase card form will appear.

Click function button → then click undo receipt

now u can change the currency. status should be open of that PO

No…Boss…Some of the received items sold out…Undo is only possible if the remaining quantity equals to PO qty know…Thats the case…

I hope,There is no shortcut way for that, you need to reverse all the documents .