You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I aid you today?

USER: I want to change my existing reservation owing to an emergency.

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

USER: My name is Mark Hall.

ASSISTANT: There is no reservation found under your name to change.

USER: Thank you.

ASSISTANT: Thank you for choosing us.