The service listview is found on the Case Profile towards the bottom of the page, above notes & documents.
When a scheduled service has happened (or canceled, or missed…), or if you need to make changes to an existing service, you can edit the Service by clicking it from the Services Tab.
On the Summary Page for the selected service, click Edit [Service Name] in the sidebar. On the following page, you can update the appointment status as well as update/edit any other pertinent information for the service.