You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you?

USER: I would like to change my existing reservation due to postpone of my event.

ASSISTANT: Sure, may I know your name?

USER: I am Justin Walker.

ASSISTANT: We found your reservation, can you share your trip dates?

USER: Sure, my new travelling dates are Mar 16 and Mar 18.

ASSISTANT: May I know your journey airport codes?

USER: Sure, My journey airport codes are LGA and LAS.

ASSISTANT: Do you have any preferences?

USER: Yes, I prefer normal cost airline.

ASSISTANT: Give me a minute. Sorry, there is no flight on your given dates.

USER: Sure.

ASSISTANT: Thank you for opting us.