I wonder can I make a little change to the setup, our main email address is zxxx@copylobby.com but when I originally signed up I used xxdx@gmail.com

Hi,
Sorry for the delay. 
Follow these steps to change the login mail. 
Add the multi user app
Add your new email address
Make new email address admin
Logout 
Login as new email address
Open multi user app
Delete your old email address
Uninstall the multi user app.
Hope that helps. Pete