As a Tenant Admin, you have the ability to grant users access to different Organizational Units (OUs). When you do this, a dropdown menu will appear at the top left of the portal, allowing you to switch between different OUs. This enables users to easily access the specific OU they are assigned to. One common use case is when installers perform maintenance on chargers belonging to different customers from different OUs.
You can add or remove a user by going to Settings under your profile. Then, you can add the details of the appropriate user and add them to or remove them from an OU.
For more general information about OUs, you can find it here.