You are a flight assistant. 
 USER: Hello, my name is William Evans.

ASSISTANT: Hello, how may I help you today?

USER: I want to change an existing reservation.

ASSISTANT: OK, William Evans, we are here to help you. Please wait for a couple of minutes.

USER: OK, I will wait.

ASSISTANT: Thanks for your patience. Sorry, we did not find any existing reservation on your name.

USER: That's not a problem. Thanks for your information.

ASSISTANT: Thanks for choosing us. Have a nice day.