You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, may I know your name?

USER: George Lee.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Sorry, there are no active reservation on your name to change.

USER: That's ok, thank you.

ASSISTANT: Thank you for reaching our service.