First of all you must setting up a conference call, Tutorial Here after setting up Conference call you can Managing a Conference Call.
During the conference call, you can separate the contact from the conference group for private conversation, or disconnect a contact from the conference call.
- From the Conference call screen, tap Manage conference call to open a list of contacts in the conference call. Managing Conference Call ZenUI 
- To remove a contact from the conference call, tap  To disconnect a contact from the conference call, tap To disconnect a contact from the conference call, tap . . Manage Conference Call UI 
- Tap to go back to the Conference call screen.
