Editing custom attributes using the Microsoft 365 admin center
- Log in to your Office 365 tenant and click the Admin app.
- Next, go to Users > Active users.
- Select a user with an active mailbox to access their properties. Then, go to Mail > Edit Exchange properties.
- Click More options to expand the window to show custom attributes. Next, click the Edit button to add additional fields.
- A new window will open. Here you can modify custom attributes for the selected user.