You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I want to change my existing reservation. Could you help me with that?

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

USER: William Harris.

ASSISTANT: Please wait for a moment.

USER: OK.

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

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for approaching us.