You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you today?

USER: I want to change my existing reservation due to some health issue. Can you help me?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Yes, I am Samuel Thompson.

ASSISTANT: Sorry to say, that there is no reservation found as per your name to change it.

USER: Ok, not a problem. Thank you for your information.

ASSISTANT: You are welcome always.