You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

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

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

USER: Myself Gregory Wilson.

ASSISTANT: Sorry, there is no reservation found on your name in our database to change.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for reaching us.