Step 1: Sign in to your Google Admin console.
Step 2: From the Admin console dashboard, go to Users.
Step 3: Click a user's name to go to their account page.
Step 4: On the user's account page, click the Account section.
Step 5: Scroll to the Aliases section. Then click Remove next to the alias you want to remove.
Step 6: Click Save changes.
[Note It can take up to 24 hours for the alias to be removed]