Reverse an Invoice payment

How do I reverse an invoice payment, I had 2 amounts owing on 2 different invoices and credited the wrong Invoice. Now I have to reverse the one amount ???
So I have the paid in full tag on the incorrect invoice?? which is in effect not yet paid.

If this is just your entry error, just edit the payment to allocate to the correct invoice.

This is what I did and I do not seem to be able to reverse it.

I opened my Invoice and at the top right
I went to “Receive money” and simply selected “Customer payment into Cheque Account”, as I always do, but now I need to reverse it

Go to the Bank Transactions tab. Click Edit for the transaction. Change anything you want and click Update, or click Delete.

I do not seem to be using the “Bank Transaction” facility.
If I go to the Invoice and try and edit the invoice, the program does not let me edit, or change a value. I am using Manager version 17.1.33 and I only have one Business and I only invoice about 3 invoices a year.
My problem is that I need to send a statement for the outstanding amount.

Sorry I mean 30 Invoices a year, I am a retired Engineer and I consult from time to time so I can use tipex and PDF editor if I need to.

Ok so you are using an older version.
Go to the Bank Account tab, click on the bank account balance (blue figure - rhs) and you should see a list of transactions, click on Edit next to the transaction that needs correction. Make your correction and click Update at the bottom.