You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, I will help you to change your reservation. Please mention your name.

USER: Mary Hill.

ASSISTANT: Ok, please allow me a moment.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your name to change your reservation.

USER: That's ok, no problem. Thank you.

ASSISTANT: Welcome, have a nice day.