You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Scott Wilson here.

ASSISTANT: How may I assist you?

USER: Please change my existing reservation.

ASSISTANT: Sure, please wait for a moment to check your details.

USER: Sure, take your time.

ASSISTANT: I have found your reservation, can you help me with your travelling airport codes?

USER: My locations are from SFO to PHL.

ASSISTANT: May I know your travelling dates?

USER: My planned dates are from 10/21 and 10/23.

ASSISTANT: Sorry, no flight is available for you.

USER: It's ok, thanks for your information.

ASSISTANT: Welcome.