You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello,. May I know your name?

USER: My name is David Wilson.

ASSISTANT: How can I help you now?

USER: I just want to change my existing reservation.

ASSISTANT: OK, please wait for moment while I check.

USER: OK.

ASSISTANT: Thank you for waiting, sorry to inform there is no any reservation on your name.

USER: Thank you, for giving information.

ASSISTANT: Thank you, have a nice day.