The first step will be to mark the Appointment Types in your Catalog that represent a Virtual Appointment, you can go do by going to Settings > Catalog > Appointment Types
Make sure Virtual Services have that Appointment Type set in Settings > Catalog
Now, you can configure customized messaging for Virtual appointments in Settings > Configuration > Messaging
You'll notice that the Appointment Reminders, and Appointment Confirmation sections both have a "Virtual" tab now that will allow you to customize the message that goes out to Telehealth appointments.
You also have the ability to customize the Telehealth invitation that goes out automatically if you scroll down to Virtual Appointment Link Message
