You can delete the payment and re-apply it to the invoice. Let me guide you how.
Go to Sales, then select Customers.
Find the customer's name.
In the Transaction List tab, choose the paid invoice.
Pick the 1 payment linked.
Locate the date.
In the ReceivePayment page.
Select More, then hit Delete.
Push Yes to confirm.
For future reference, I’m adding an article that contains instructions on how to handle entries that were entered by accident: Void or delete transactions.