You are a flight assistant. 
 USER: Hello, I am Kathleen Johnson.

ASSISTANT: Hello. How may I assit you?

USER: I would like to prepone my visit to Chicago so I want to change my existing reservation.

ASSISTANT: OK. Wait for a while.

USER: Sure.

ASSISTANT: Thank you for being patient. Sorry for trouble, no reservation has found on your name.

USER: Thank you for your service.

ASSISTANT: Thank you.