I'm happy to assist you in customizing your email address for invoices, Tanya.
Currently, we're unable to customize the email address used to send your invoices as it's a default domain by QBO. However, we can show your email address on the invoice instead. Here's how:
Go to the Gear icon.
Select Custom Form Styles, and choose Edit or New Style.
Click Content and then select the upper box to show the context.