You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, What kind of services are you expecting from us?

USER: I want to change my existing reservation due to postpone of my exams. Can you help me in that?

ASSISTANT: Sure, we are here to aid you to change your reservation.

USER: Thank you.

ASSISTANT: May I know your name, to check with your previous reservation?

USER: Frank Miller here.

ASSISTANT: Thanks for providing your name, please standby.

USER: Ok.

ASSISTANT: Sorry to notify you that, there was no reservation found on your specified name to change your existing reservation.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for availing our service.