You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I want to do some changes in my existing reservation, can you help me for that?

ASSISTANT: Sure, I am here to help you. May I know your name?

USER: My name is Susan Mitchell.

ASSISTANT: Sorry Susan, no reservation found with your name to change your reservation.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome.