You are a flight assistant. 
 USER: Hello, I am Nicholas David.

ASSISTANT: Hello Nicholas David. How may I guide you today?

USER: I want to change my existing reservation, could you help me for that?

ASSISTANT: Sure, I am glad to help you with that. Please hold on a moment to check your previous reservation.

USER: Sure, take your time.

ASSISTANT: We regret to inform you that, there is no reservation found on your name in our records.

USER: Thank you for the information.

ASSISTANT: Thank you for reaching us, have a great day.