You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am David Allen. I would like to change my existing flight ticket. Could you help?

ASSISTANT: Sure, please hold on for a moment.

USER: Sure, please take your time.

ASSISTANT: I am sorry, there are no reservations with your name.

USER: Ok, thank you for the information.

ASSISTANT: Thank you, have a good day.