You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I aid you?

USER: I want to change my existing reservation due to bad health issues.

ASSISTANT: Sure, I am glad to help you. May I know your name?

USER: I am William Miller.

ASSISTANT: Sorry, there are no reservation found on your name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for choosing us.