Hi @Chris26 and welcome to the Forum! 
If you wish to switch the primary domain associated with your Organization, and to help facilitate this change, I first recommend you to add your new email address by following the directions on our guide that explains how to add a new email address to your Asana account
Then, as @Jason_Woods explained, you’ll need to contact our support team who will help you to make the corresponding changes to your Organization.
Hope this helps! Let me know if you have any follow-up question!