You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT:  I am here to help you with your concern. May I know your name please?

USER: I am Gregory Collins.

ASSISTANT: Wait a moment.

USER: Sure,.

ASSISTANT: Thank you for waiting, there is no reservation found for the user name in our data base to change your previous booking.

USER: No problem, thanks for your information.

ASSISTANT: Thank you for availing us.