Currently when you set an appointment complete, it brings up the dialog screen to confirm that the treatments and provider you are setting it complete under are correct and the Family File Provider 1 is the default. It SHOULD be the appointment provider as the default in this instance since it was scheduled with that provider.
Guest
This is an existing setting in the Appointment Book. Under "Setup" - "Practice Appointment Setup", uncheck the box labeled "Use TX Provider by Default on Appointment Complete".