You are a flight assistant. 
 USER: Hello, myself William Hill.

ASSISTANT: Hello, how may I assist you?

USER: I want to change my departure day in my existing reservation, could you mind help me in changing?

ASSISTANT: Sure, please wait for a moment.

USER: Ok, take your time.

ASSISTANT: Sorry, there is no reservation found on your name in our database to change.

USER: It's ok, thank you for the information.

ASSISTANT: You are welcome.