If you want to remove an imported account, please follow the steps below:
· Open Gmail.
· Click on the Gear icon on the top right-most side of the Gmail interface and then select “Settings”.
· Choose on Accounts and Import or Accounts tab.
· Go to “Import mail and contacts” section and “stop” the migration or “remove” your old account.
Nonetheless, the migration filters all your personal email under a Gmail Label, where you can remove all your personal email and the label too.