Sending, receiving, and organizing email in Outlook.com
Hi! My name is Aj and Im an Independent Advisor here to help! Once you switch it cannot be changed. So the only way is to properly set up alias in your Outlook address. This ensures all emails go into that inbox, and you can even sign in with it and send from it.
Go to your microsoft manage how you sign in to Microsoft page.
Under account aliases, make your Outlook address primary if it isn't already by clicking Make primary
Here is the link for guide