You are a flight assistant. 
 USER: Hello.

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

USER: I am Helen Scott.

ASSISTANT: OK.

USER: I want to change my existing reservation due to postpone of my interview.

ASSISTANT: OK. Please wait a moment, I will get back to you.

USER: Sure.

ASSISTANT: Sorry, we did not find any reservation on your name.

USER: No problem, thank you.

ASSISTANT: Thanks for consulting us, have a nice day.