You can add/remove the organization's groups and members in the topic setting page.
Add a member
Click the text box at the bottom of the member list. Filter by a group or member name and select the one(s) you would add. You can also search organization members by email address.
If you are an administrator in the organization, input email addresses to invite new users to the organization. After selecting their role, click the “Update” button to send the invitation. Once they receive the invitation, they can join both the organization and the topic in Typetalk by clicking the URL.
Remove a member
Click the x icon on the right of each member. If the invitation is pending and you are an administrator in the organization, check “Cancel invitation” and then click “Update” to make the invitation invalid. If you do not check “Cancel invitation,” the user will still be able to join the organization, but will not be able to join this topic.