1. Go to Master Data -> Clients -> User -> Choose a user -> open tab "Others"

2. In the field "AppointmentScheduleGroup" push the button create

3. In the new mailing list you fill the mandatory fields but not the identifier: name, type - internal and you check the active flag

4. Push button Save from the right corner and a identifier number will be generated 

5. Note the Identifier because you will use it later