It is fairly straightforward to change who your Outlook 365 supplier if you can log into the Outlook 365 admin centre with an admin account.Log into the Outlook 365 admin center and then follow the instructions on this page:https://docs.microsoft.com/en-us/office365/admin/misc/add-partner?redirectSourcePath=%252fen-us%252farticle%252fAuthorize-or-remove-partner-relationships-201ccb3b-6011-4bf1-a6b2-84e7cc1ee2d0&view=o365-worldwideScroll down to the section entitled: Change the partner for a subscription