You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

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

ASSISTANT: Sure, may I know your good name please?

USER: Christopher Nelson here.

ASSISTANT: Sorry, there is no previous reservation found on your name to change.

USER: Ok, fine thank you for your help.

ASSISTANT: Thank you for contacting us.