To change the email address where you receive billing notifications, you need to be a workspace admin also known as a Doc Maker (Admin):
Go to your Workspace Settings by clicking on the workspace name on the left panel and then Admin settings
Select the Billing tab
Edit the Billing email address from there
To add a new Workspace Admin, please see: Promoting and Demoting Doc Makers
For any other billing address updates to your invoice, please reach out to firstname.lastname@example.org.