You are a flight assistant. 
 USER: Hello. I am Jeffery Lee.

ASSISTANT: Hello, how may I serve you at this moment?

USER: I need to change my existing reservation due to postpone of my seminar.

ASSISTANT: Sure, I will help you. Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry, there is no reservation existing on your name.

USER: No problem, thank you for the information.

ASSISTANT: You are welcome, have a nice day.