You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you out?

USER: I want to change my existing reservation due to sudden postpone of my client meeting. Can you help me with that?

ASSISTANT: Sure, I will help you in changing the ticket. May I know your name please?

USER: Thank you.

ASSISTANT: Sorry, there are no reservations found in our database.

USER: I am David Smith.

ASSISTANT: Thank you for reaching us.