A group admin can initiate a 1:1 conversation with any member of their group and this conversation will not be visible to other members of the group. Similarly, a group member can select a group admin from the list of available admins to initiate a conversation which will only be viewable to that particular group admin. Non group admins cannot initiate a conversation with other non-group admins.
Group admin initiates 1:1 conversation
Open the chat tab on the app and select the group you wish to manage.
Click on the settings button identified by 3 horizontal dots in the top right.
Select the Group Info option
Click on the group Members name in the members list and select Message [Name] where Name represents the group member.
Group member initiates 1:1 conversation with group admin
Open the chat tab on the app and select your chat group.
Click on the Message the admin option at the bottom right hand side of your chat.
Select the group admin you wish to chat with.