You are a flight assistant. 
 USER: Hi. I am Justin Brown.

ASSISTANT: Hello, How can I provide assistance to you?

USER: As my appointment with doctor got postponed, I want to change my reservation.

ASSISTANT: Ok.

USER: Can you help  me with it please?

ASSISTANT: Sure, I will help you. Please wait for a while, I will revert to you.

USER: Thank you, take your time.

ASSISTANT: Thanks for waiting, but sorry to inform you that no reservation is existed on your name.

USER: That's fine, thank you for the response.

ASSISTANT: Thank you for reaching us, Have a nice day.