At times, you may want to allow another user to manage aspects of the Office 365 service for you. To achieve this, you will need to assign them an administrative role within Office 365. During user creation, you can grant the user an admin role, however you can also add a role to an existing user.
You should only assign a user a role that meets the minimum requirements for the access they need. A list of roles available can be found here.
New administrator roles should be added by an existing Global Admin.
Add an Admin Role to a User
It may take a short while for the administrator options to appear for the user