How to set i_channel_join_power permission in a channel group

Hi
I am a newbee so please bear with me.
From the forum discussion I understand that in order to create channels that can be only accessed by specific channel group I have to use the i_channel_join_power.
My problem is what while I can find this in the GU for the Channel, I can not find it in the GUI for channel Group.
So how do I exactly set the i_channel_join_power for a channel group?

thanks

How to set i_channel_join_power permission in a channel group