You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Can you change my existing booking?

ASSISTANT: Sure, can I know your name please?

USER: My name is Shirley Brown.

ASSISTANT: Brown, can you provide your destination and journey details?

USER: My destination is CO - DEN and source is IL - ORD. My travel dates are 07/03 and 07/05.

ASSISTANT: Give me a moment.

USER: OK.

ASSISTANT: Sorry Brown, I didn't find any flight regarding with your details.

USER: Thank you for your information.