I have a sales journal nominated in the base currency (GBP).

I create an invoice nominated in Euro. and get payed on a Euro bank account.

In the sales journal, this movement is recorded in GBP at the currency rate set in the table "currencies". and reconciled.

I need to modify this recorded GBP amount for both the invoice and the payment. To reflect a set exchange rate.

What would be the way to do that?

TIA