You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you?

USER: Charles Martin here. I would like to change my existing reservation due to my trip dates are postponed.

ASSISTANT: Sure, I will help you. Please wait for a moment. I have found your reservation, may I know your new travel dates?

USER: I would like to take off on 10/28 and return on 10/30.

ASSISTANT: Please send your nearby airport codes.

USER: My source and destination airport codes are SFO and PHL.

ASSISTANT: Please wait for a while.

USER: Sure, I will wait for your response.

ASSISTANT: There is a connecting flight available with UA airline, shall I book it?

USER: I need a direct flight.

ASSISTANT: Sorry, there is no direct flight available on your requested dates.

USER: It's ok, thank you for giving information.

ASSISTANT: You are welcome, have a nice day.