You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this time?

USER: I want to change my existing reservation, can you please help me out in that?

ASSISTANT: Sure, I will help you. May I know your name for checking your previous booking?

USER: Myself Samuel Green.

ASSISTANT: Please wait for a moment.

USER: Sure.

ASSISTANT: Sorry Green, there is no reservation found on your name to modify it. Thank you for your time in reaching us.

USER: Oh! That's fine I'll choose other way to travel. Thank you for helping.

ASSISTANT: Have a nice day.