I know how to change the customer on a sent invoice, Rocky. Let me walk you through this process.
If you've already sent the invoice to one customer and need to send it to a new customer, you can duplicate the invoice transaction. This will allow you to keep a record of the original transaction and any changes you make.
Here's how:
Go to the Sales menu from the left navigational panel, then click All Sales.
Find the invoice transaction by clicking the Customer dropdown, then enter the customer's name.
Locate the transaction, click the dropdown beside the Receive payment, and choose Duplicate.
Click the dropdown, then select your customer's name.
Enter your customer's email.
Review the changes you've made, click Save and Close or Review and Send, then click Send Invoice.