You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I assist you?

USER: I want to change my existing reservation, as my exam got postponed.

ASSISTANT: Sure, may I know your name?

USER: I am Christopher Turner.

ASSISTANT: Ok, please wait a moment.

USER: Ok.

ASSISTANT: Sorry, there is no existing reservation on your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thanks for choosing us.