You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I accidentally booked a ticket and now I want to change the reservation. Would you help me out?

ASSISTANT: Sure. May I know your name?

USER: It's Dennis Johnson.

ASSISTANT: Sorry, there is no reservation found Dennis.

USER: That's OK. Thank you for your time.

ASSISTANT: My pleasure.