You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: I am Patrick Young. I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, please allow me a moment to check for your status.

USER: Sure.

ASSISTANT: I have found a reservation, may I know your planned airport codes and dates?

USER: I would like to travel on Sept 12 and return back on Sept 14.

ASSISTANT: Do you have any specifications?

USER: My depart time is evening.

ASSISTANT: Please provide me the airport codes.

USER: I am planning to book a ticket from AUS to SFO.

ASSISTANT: Sorry, there are no flights available for your desired dates.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for reaching us.