You can update any person's information from diio settings.
Go to diio settings → People.
Click on the person in the list.
The person's profile has the Profile, Permissions, Settings and Teams tabs. In Profile you can edit the Segment (the name can't be edited). In Teams you adjust their teams and team roles, and in Permissions their administrator roles (a tab visible only to the Main Administrator and not available on the Starter plan).
Click "Save changes" on each tab you modify. Changes take effect immediately.