You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you out?

USER: I want to change my existing reservation. Can you please help me with this?

ASSISTANT: Sure, I will help you in changing the ticket.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Sure, my name is Mark Davis.

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

USER: Ok, no problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you for checking.