You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you today?

USER: I am planning to change my existing reservation. Can you please help me for this?

ASSISTANT: Sure, may I know your name please?

USER: Myself Brian Campbell.

ASSISTANT: We found a reservation in your name. Can I have your airport codes?

USER: Sure, my airport codes are LAS to EWR.

ASSISTANT: Help me with the trip dates?

USER: I am planning my trip on Mar 3 and again I will return back on Mar 5.

ASSISTANT: Do you have any preferences?

USER: My return time is evening.

ASSISTANT: Sorry, no flights were running in your desired routes.

USER: Not a big problem, anyhow thank you very much for your kind information.

ASSISTANT: Thank you for reaching us.