CloudM Manage has only 1 domain administrator. However, it can have multiple administrators.
CloudM Manage will provide by default an admin role to any user with an admin role in G Suite. However, if you wish for a more personalised admin role, then you can create a custom role.
Therefore, to add another administrator to CloudM Manage, you can give a user admin privileges on G Suite, or create your own role and assign it to the user.