You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I am Larry Wright.

ASSISTANT: Nice to meet you Larry.

USER: I want to change my existing reservation, due to some health issue. Can you please help me out?

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

USER: Thank you.

ASSISTANT: Please wait for a moment.

USER: Ok, take your time.

ASSISTANT: I have found your flight reservation. Please tell me your airport codes?

USER: My new travelling airport codes are from SFO and CLT.

ASSISTANT: Now please share your travel dates?

USER: I am planning to start my journey on 09/24 and return back on 09/26.

ASSISTANT: Please wait for a moment.

USER: Ok, take your time.

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

USER: That's ok, thank you for checking.

ASSISTANT: Thank you.