You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. I hope you are good toady, how can I help you?

USER: William Moore here.

ASSISTANT: Ok.

USER: I want change my existing reservation due to my grand father health issue, hope your helping me out.

ASSISTANT: Sure, I will help you with that. Please wait for a while. Sorry William, there is no reservation found on your name.

USER: Ok, no issues. Thank you for checking.

ASSISTANT: You are welcome, have a nice day.