You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Due to change in my plans to visit Dallas, I would like to change my existing reservation. Can you help me with this?

ASSISTANT: Sure, I will help you. May I know your name please?

USER: My previous reservation has done with my name Sarah Carter.

ASSISTANT: Please wait a while.

USER: Sure.

ASSISTANT: There is reservation on your name, please share your travel dates?

USER: My preferable journey dates are from 08/30 to 09/01.

ASSISTANT: Please may I know your airport codes?

USER: My nearest airport codes are from OAK to SFO.

ASSISTANT: There is no flight available in your desired travel dates.

USER: Ok, not an issue. I will find any alternate for this trip.

ASSISTANT: Thank you for opting us.

USER: Thank you for providing information.