First of all you have to be switched to organization app see Switch account.
Adding or removing members of an organization can be done in the organization settings (bottom bar – click on name of organization). Tab “Organization members”
- By filling in the email and roles, and then clicking on “invite”, you can add new members to the organization
- Using the red cross on the right, members can be removed
- In the drop-down menu, the role of a member can be changed