R12.1.3 Purchase orders which are received,matched to Invoice and status is closed with Incorrect Am

We are on 12.1.3 and went live couple of weeks back in Purchasing.

Below is the scenario

1.Created a PO with quantity as 1 and purchase price as 1570.42 (incuding GST) and it should have been 1413.38 only

2.Received the PO .

3.Created an AP invoice for amount of 1570.42 and matched the PO.

4.PO header status is Approved, Closed,line status is Closed

Realized that the Tax amount should have been excluded from the PO price.

Question

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How to do we Unreceive the items, change the amount and then receive again?