Can somebody help me on this pls !!

It's not possible

You won't be able to change the invoice currency that the PO module created so you will need to design a process of exporting the AP invoices and replacing the invoices with new ones. Make sure that you're audit trail is strong.

What is the purpose of the request?  Why do you want it in functional currency?  Is it just to see the balance?  If so Am I misunderstanding?  When an invoice is entered in a source currency, it is automatically converted to the functional currency, you can run your aged trial balance and show the invoices in functional currency.  In Customer Inquiry, you can see the functional value.  What more do you want/need?

Thanks Eva. I explained the same to the client and did a sample transaction , then they were okay with the process , Cheers for the input , Appreciate !!!

Thanks Jay , As Always !!!