How do I change an email address on an existing invoice

Hello info1911

Thanks for joining the Community. 

You can update the email by opening the invoice and editing the email field. To help locate the invoice, type the invoice no. into the search bar (click the magnifying glass in the top-right corner of QuickBooks). If you'd like to update this for all future correspondence to this customer, you can edit their info by navigating to Sales > Customers (take me there) > Select the customer from list > Edit > See email field > Save.