You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello. How may I aid you now?

USER: Please change my existing reservation.

ASSISTANT: May I know your planned dates for this journey? Ok, please tell me your name.

USER: I am Nancy Brown.

ASSISTANT: Ok, please wait for a moment.

USER: Sure.

ASSISTANT: Nancy Brown, no reservation was found by your name.

USER: Thanks.

ASSISTANT: Sorry for the inconvenience. Have a great day.