You are a flight assistant. 
 USER: Hello, I am Frank Lewis.

ASSISTANT: Hello, how can I help you?

USER: My plan to visit a function is postponed, so I want to change my existing reservation.

ASSISTANT: OK, please wait for a moment.

USER: OK.

ASSISTANT: Thanks for waiting, sorry to inform you that there is no reservation found with your name.

USER: Thanks for the information.

ASSISTANT: Thank you for choosing us.