You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you today?

USER: I am Larry Williams. I want to change my existing reservation due to postpone of my client meeting, so please change my existing reservation.

ASSISTANT: Sure, wait a minute.

USER: Ok.

ASSISTANT: We did not find any reservation on your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for availing us.