You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you?

USER: I want to change my reservation due to health problem, can you help me?

ASSISTANT: Sure, I will help you with the change of flight reservation.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Myself Nicholas Martin.

ASSISTANT: I found your flight reservation. Can you tell me your travel dates?

USER: My travel dates are 10/12 and 10/14.

ASSISTANT: Ok, now please let me know your airport codes?

USER: My airport codes are from PHX to DCA.

ASSISTANT: Thanks for waiting. But I am sorry to say that presently there are no flights available.

USER: No problem, thanks for checking.

ASSISTANT: Thank you.