You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you at this moment?

USER: Please change my existing reservation due to some health issues?

ASSISTANT: Sure, I am happy to help you with this flight ticket booking. Can I have your good name please?

USER: Sure, I am Mark Campbell.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Sorry Mark Campbell, no reservation has found under your name to change.

USER: Ok, not an issue. Thank you for your information.

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