You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello,. How can I help you?

USER: My name is Robert Barker, I want to change an existing reservation.

ASSISTANT: OK, Sure I will check it and revert you back.

USER: OK,.

ASSISTANT: Sorry, There is no reservation found on your name.

USER: OK, Thanks your information.

ASSISTANT: Thank you. Have a good day.