You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. May I know your good name please?

USER: I am Carol Green.

ASSISTANT: Ok Carol, how can I help you?

USER: Due to some reasons my trip has been postponed, so I want change my existing reservation, can you please help me?

ASSISTANT: Sure, please give me a second.

USER: Ok.

ASSISTANT: Sorry, there is no existing reservation on your name.

USER: Thank you for your service.

ASSISTANT: You are welcome.