You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, How may I help you?

USER: I want to change my existing reservation due to illness.

ASSISTANT: Ok, please provide me your name to check with details.

USER: I am William Miller.

ASSISTANT: Thanks for waiting,unfortunately no flight on under your name.

USER: Ok, no problem. Thank you for helping me.

ASSISTANT: Thanks for choosing us.