You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you today?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, I will help you with that. Can I know your name to check your previous reservation?

USER: I am Christopher Perez.

ASSISTANT: Please wait a moment to check.

USER: Ok.

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

USER: Ok, no problem. Thank you.

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