You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Gary Green.

ASSISTANT: Green, how may I assist you today?

USER: Actually, I am planning to change an existing reservation, can you help me out?

ASSISTANT: Sure Green. Sorry, no reservations with your name Green.

USER: That's fine. Thank you for your help.

ASSISTANT: It's my pleasure Green.