Go to the Brand Settings section, where you'll see the list of current brand users and their status (Enabled for active users, Pending for users who haven't accepted their email invitation).
Click on the “Add Brand Users” button to the right of the search bar.
To add an existing user:
Start typing the name or email in the search bar.
Click "Add To Brand" on the right of the creator you'd like to add.
To invite a new user:
Click on the "Invite New BrandUser" button in the top-right corner.
Type in the email address of the user you'd like to invite.