This is the short version of a very long story. I have/own a domain called "mine.com" (example) It is a GoDaddy managed domain and the domain manager in O365 is all set up and showing it as the default. When I got these O365 business subscriptions, I had to go through some silly hoops and ended up using boxigloo to get through the process. If I remember it was the onmicrosoft.com registration process.
What I want to do now is simply get off this onmicrosoft subdomain so I can properly set up SharePoint. I want SharePoint to be mine.sharepoint.com vs. boxigloo.sharepoint.com.
Is there a way to reset my O365 instance to use the domain I own for everything and get rid of and vestige of the subdomain?