How can I change our email address that is currently displayed in the invoice layout?

At the bottom of the invoice layout, the default email address of the relation you created for your own company is used.

In the Extra menu, go to Locations first. There you can find out which relation number is used for your location.

Then, search for the relation with this relation number in the Relations module.

On the Contact Information tab, you can edit the email address. Please note that the email address marked as "Default" is the one that will be displayed.

When you print an invoice again, the modified email address will be shown.