You cannot use this Application to book an appointment at the current time.
You must contact your own Doctor or Clinician who will provide you with details.
It is totally up to your own Doctor if they want to provide services via telemedicine and using this or any other platform.
My clinician said they are not using the service, how can they join it?
It is up to your Clinician if they want to join but they are free to signup on https://www.hashealth.com