You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you for  today?

USER: I'm William Harris here, and I want to change my existing reservation, because of business deal post pone.

ASSISTANT: Please wait for a moment.

USER: Ok.

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

USER: Thank you, for your information.

ASSISTANT: Thank you for choosing us.