Many thanks for your post.
To be able to see who deleted an appointment you will need to run the Audit Log.
From the main menu of R4 select Utilities, once in that list you will see an option for Display Audit Log.
From here you can filter the time and actions, I would recommend that you change the action to Deleted Appointment. Then select the date range. Please note that its the range of when the task was completed not the appointment.
This will then show you when an appointment was deleted and by who, you can print the report via the top left option.
Hope this helps.