How to change exchange rate on payment entry?

Hello, I’m using erpnext v13.28.0 now and my problem is:

For example:
I purchase USD 100 product from A company and we have 30days credit, and we are using GBP change to USD to pay it. Today(Purchase invoice date) exchange rate is 1.22, but after 30days the exchange rate might change to 1.25etc. When I go to purchase invoice->create payment (payment entry), we cannot edit the exchange rate from 1.22 to 1.25, and the recorded amount will not match my bank slip.

I found 1 method for this case is cancel the purchase invoice first and amend the exchange rate from 1.22 to 1.25 then process payment entry. But if the invoice have partial payment eg. 30% deposit etc. then we cannot use this method.

Is there any method that allow us to edit exchange rate in payment entry page?
(I found V12 have this function but V13 have not?)

Thank you.