PLEASE HELP Pmt posted - wrong exchange rate

I posted a payment for a Invoice at the wrong exchange rate and want to reverse the payment. I know how to put a reverse journal through in the payments journal, but that does not an unapply/open the invoice so tat I can re-select it for payment at the correct exchange rate. From what I read on the forum thus far, one cannot unapply in verions 3.7 and earlier. I am using Version 3.6 How do I rectify the exchange rate - If I put adjustments through to the Accounts Payable, Foreign Capital Gains and Bank Accounts respectively will anything else be effected? What should I do please!

Couldn’t you just run the “Adjust exchange rates” under GL > Periodic activities? Karl