I have entered the wrong invoice as paid how do I change this?

Hello and Welcome to the Community, billy16 👋

To correct this, please locate the payment from the customer's transaction list (Sales > Customer > Select customer) and then delete this on the action drop-down. 

This will then remove the payment from the invoice, leaving this as open, and you can record the payment against the correct invoice. 

If you matched the payment from the banking screen, you'll see the payment again in the 'For-Review' tab ready to be matched - click 'find match' to see all matching options. 🙂