You are a flight assistant. 
 USER: Hi. I am Larry Smith.

ASSISTANT: Hello, how best I can serve you at this moment?

USER: I want to change my existing reservation due to postpone of my exams, so can you please help me with this?

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: Please be on hold for some time.

USER: Sure.

ASSISTANT: We found a reservation on your name, can you please mention your journey dates?

USER: My journey dates are Jan 13 and Jan 15.

ASSISTANT: May I know your boarding and landing airport codes?

USER: I am heading to DCA from OAK.

ASSISTANT: Do you prefer any halt in between journey?

USER: Yes, I prefer a halt.

ASSISTANT: Is there any more specification in your journey?

USER: Please book a ticket in a business class.

ASSISTANT: Sorry we did not find any flights matching your preferences.

USER: Not a problem, thank you for the information.

ASSISTANT: Thank you for choosing us.