The Assign to Organization feature allows updating of multiple users' Branding Organization assignments at once.
Adding Multiple Users to a Branding Organization
Navigate to the User List under Admin > Users.
In the User List, the desired users can be narrowed down using a query by clicking on the Filter button and selecting Advanced or a specific user can be searched for.
When the Advanced Filter is selected, the User Filter allows Admins to create specific queries.
Once the desired list of users is displayed, click the checkbox to the left of the Student header to select all users. Click the More button > Assign to Organization.
From the Assign users to organization pop-up, select the desired Branding Organization and click the Update button.