Yeah it's not in there. But you create this user in CUCM under User Management > Application User.
Depending on your CUCM version the 'user group' referenced may actually be called/termed an 'Access Control Group'. I think this changed in CUCM 9.1 or so.
The references to assigning the rooms and endpoints mean Device Association to the application user in the Application User page, not Owner ID on the Device > Phone page.
NPM