To completely sign out of an account, you'll have to close all the Office programs you're running when you responded Yes to removing your account.If you're signed in with more than one account, you'll have to sign out of each one.You can sign in again with an account you signed out of. Go to File > Office Account > Switch Account. However, Office will treat it as a new account, meaning you'll have to set customizations all over again.See More...What is Microsoft 365 admin?
Microsoft Office 365 admin roles give users authorization to perform certain tasks in the Office 365 admin center. Only the global administrator can assign or modify an admin role, which grants the permissions required to control certain functions in Office 365.What is Office 365 admin portal?
Office 365 Admin Portal – this is the main portal for managing an Office 365 tenant, providing admin controls for a variety of common tasks such as managing users, groups, and billing, as well as other features such as the Service Health Dashboard.