You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, welcome to ABC flight ticket booking agency. How may I help you?

USER: Due to heavy snowfall in Oakland, which I would like to visit with my friends, now I would like to change my existing reservation. Will you help me with this?

ASSISTANT: Sure, may I know your good name please?

USER: My name is Rachel Hernandez.

ASSISTANT: Sorry to inform you that there is no previous reservation found n your name to change.

USER: Ok, no problem, may be there is a mistake during my previous booking.

ASSISTANT: Thank you for approaching us.

USER: Thank you for providing information.

ASSISTANT: Have a good day.