You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you with today?

USER: My name is Shirley Roberts. I have postponed my holiday trip, could you please change my existing reservation?

ASSISTANT: Sure, I can help you with that. Can you please help me with the source and the destination airport codes?

USER: I would like to travel from CLT to SEA.

ASSISTANT: Shirley, could you please provide your travelling dates?

USER: My departure date is 09/26 and return date is 09/28.

ASSISTANT: Ok, let me check for the availability of flight.

USER: Ok.

ASSISTANT: Shirley, I am sorry to inform you that there is no flight available at your requested dates.

USER: That's ok. Thank you for the information.

ASSISTANT: You are welcome. Thank you for contacting us.