You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Robert Lee.

ASSISTANT: How should I help you now?

USER: I have a change in my plan. I want to change an existing reservation.

ASSISTANT: Sure, please wait a moment. Thank you for waiting. Sorry Lee, there is no reservation found with your name.

USER: Ok.

ASSISTANT: Thank you for choosing us.

USER: Thank you.

ASSISTANT: You are welcome, have a good day.