All board followers are members of all topics by default. As a board owner or administrator, you can manage the topic membership at any time. This is a great way to add groups to your classroom.
To add new users to a topic:
1. Log in to a specific board.
2. At the ribbon, click “Settings” tab.
3. Click the “Topics” section.
4. Select the topic.
5. Select the followers you would want to add as topic subscriber by checking the "X" button next to follower's name. If you want to add all followers at one time, check the “X” button next to the “Topic Member”.
6. Click on "Update Topic".
You can undo the changes you have not saved by clicking the “Cancel Changes” icon.