You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I am David Turner. I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Yes, I can help you. Sorry to inform you that there is no reservation found on your name.

USER: That's fine. Thank you for your service.

ASSISTANT: Thank you for contacting us.