You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

USER: I am Lisa Mitchell. I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, I am gleeful to help you to change your reservation.

USER: Thank you.

ASSISTANT: Please wait a moment.

USER: Ok.

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

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for opting us, have a nice day.