You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Can you help me out in changing my existing reservation?

ASSISTANT: Sure, may I know your name please to check whether with your name any ticket had booked or not to change?

USER: Sure, my name is Paul Brown.

ASSISTANT: Sorry Brown, there is no ticket booked with your name to change.

USER: Ok, thank you.

ASSISTANT: Thank you for approaching us.