You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you now?

USER: Due to sudden change in my schedule, I would like to change my existing reservation.

ASSISTANT: Sure, I am ready to help you with that. Can I have your good name to check existing reservation status?

USER: Myself Jason Anderson.

ASSISTANT: Ok Jason, I have found your reservation so please provide me your travel dates.

USER: My travel dates are from 07/07 to 07/09.

ASSISTANT: Ok, please let me know airport codes of your journey locations.

USER: My preferred airport codes are from CLT to MSP.

ASSISTANT: Sorry Jason, there is no flight available to you with changed details.

USER: Ok, no problem. Thanks for checking.

ASSISTANT: My pleasure. Thank you for choosing us, have a good day.