How to set a group with manager right in newly created Mailbox

hello,When I configured my Domino, the first user was considered as the main Administrator of my Notes Infrastructure. So when I create a new Mailbox, it is always added in the ACL with the Manager right.

I would like to have a group instead of that Admin User. That group will contain that Admin User. How can change my setting in order to obtain my needs?

tks