Allowing a server group to 'Assign server groups'

In teamspeak 3; I would like to know how to make a specific server group able to grant permissions. We use military ranks for Server groups and also Offices.. So say I wanted the 2Lt. server group to be able to promote people (Assign server group ranks) But I am unsure how to do that. Could I perhaps have a run down on how to do that? Thank you very much for your time.

Allowing a server group to 'Assign server groups'