To add or change the billing address for your invoices, login to your Seller Labs Account. From your Seller Labs Dashboard click on your email on the top right corner of the screen, and from the dropdown menu click on "Account". Now click on "Billing" from the options near the top of the page.

From the Billing tab, scroll down past the Upcoming Payments and Payment Method boxes until you see the Billing Address box.

Click the Update Billing Address button and a window will pop out where you can update your billing address. 

Add your billing address details then click Save Billing Address to apply the changes.

That's it! You're done.