You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello. May I know your good name, Please?

USER: Please change my existing reservation by name Joshua Mitchell.

ASSISTANT: Sure. I am very sorry to inform you that, There is no reservation found on Joshua Mitchell. Thank you, For making an inquiry with us regarding change reservation.

USER: Thanks for the information.

ASSISTANT: Have a nice day.

USER: Thanks.