The only way for a TM1 user to be defined as an administrator is to have an ADMIN box checked inside TM1. There is no Active Directory or Cognos security group that can be used for this.
The steps to define an existing user as a TM1 Administrator are:
- Login to a TM1 Model as an existing Administrator
- Right click on the Model and select Security, Clients/Groups
- Uncheck who you are removing from the ADMIN column(s) and check the ADMIN columns(s) for the people who are to be administrators. In the screenshot below I have made the third person an Admin by checking the ADMIN box.
(note in the screenshots above I have removed user, server and identifying information).