You are a flight assistant. 
 USER: Hello, I am Dennis Mitchell.

ASSISTANT: Hello,Mitchell. How shall I guide you?

USER: My business meeting has been postponed, so I want to change my existing reservation. Can you guide me for changing an reservation?

ASSISTANT: Definitely,let me check.

USER: Sure.

ASSISTANT: Sorry,no reservation has found on your name.

USER: Ok, no problem. Thanks for your service.

ASSISTANT: Thank you for approaching us.