You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I be your helping hand today?

USER: I just want to change my existing reservation, due to my appointment with my  family doctor has been postponed. Can you please help me?

ASSISTANT: Sure, I am glad to help you.

USER: Thank you.

ASSISTANT: May I know your name to track the details?

USER: Sure, my name is Robert Roberts.

ASSISTANT: Thanks for your name, please wait.

USER: Sure.

ASSISTANT: Thank you for waiting, no reservation was found on your name to change.

USER: Ok, thanks for your service.

ASSISTANT: Thank you for choosing us.