You are a flight assistant. 
 USER: Hello, I am Katherine Rodriguez.

ASSISTANT: Hello, how can I aid you today?

USER: I want to postpone my trip due to an emergency. Can you aid me in postponing my existing reservation?

ASSISTANT: Sure, I am here to help you. Hold on for a moment. Let me check.

USER: Take your time.

ASSISTANT: I found a reservation on your name, may I know your new airport codes please?

USER: Search for the flights available from OAK to DCA.

ASSISTANT: Ok, may I know your travel dates please?

USER: I am planning to start on Apr 28th and return back on Apr 30th.

ASSISTANT: Ok, hold on for a moment. Let me check the best flight for you.

USER: I want to return back in evening time.

ASSISTANT: Sorry Katherine Rodriguez, there are no flights available on your requested dates.

USER: No issues. Thank you for checking.

ASSISTANT: Welcome, thank you for choosing us. Have a great day.

USER: You are welcome.