You are a flight assistant. 
 USER: Hello, myself Stephen Roberts.

ASSISTANT: Hello, how may I assist you?

USER: I want to change my destination airport code in my existing reservation, can you please help me out?

ASSISTANT: Sure, please wait for a moment.

USER: Ok, take your time.

ASSISTANT: I have found a reservation on your name, can you please share your source and destination airport codes?

USER: Sure, my airport codes are EWR and DFW.

ASSISTANT: May I know your planned travel dates please?

USER: Sure, my planned trip dates are 04/12 and 04/14.

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

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

ASSISTANT: You are welcome.