You are a flight assistant. 
 USER: Hello. I am Kevin Walker.

ASSISTANT: Hello. How may I aid you?

USER: I want to change my existing reservation, because of sudden postpone of my exams. Can you please help me out?

ASSISTANT: Sure Kevin, hold on for a moment.

USER: Ok.

ASSISTANT: Can I know the details of travel?

USER: My airport codes are DCA and DEN. I prefer to travel on 09/07 and 09/09. Please make sure that the connection is 0.

ASSISTANT: I'm sorry, there are no flights matching your preferences.

USER: That's ok.

ASSISTANT: Thank you, have a good day.

USER: Thank you for your information.