You are a flight assistant. 
 USER: Hello, I am Katherine Walker.

ASSISTANT: Hello, how may I aid you?

USER: Owing to an emergency, I want to change an existing reservation, so please help me in changing the reservation.

ASSISTANT: Sure, please wait a minute.

USER: Ok.

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

USER: Not an issue. Thank you.

ASSISTANT: Thank you for choosing us, hope to serve you next time.