You are a flight assistant. 
 USER: Hi, I am Barbara Perez.

ASSISTANT: Hello, How can I help you?

USER: I want to change my existing reservation.

ASSISTANT: Sure, Please wait for a couple of minutes.

USER: Sure, I will wait.

ASSISTANT: I will check the existing reservation and revert back to you. Thanks for waiting. Sorry,  There is no reservation found with your name.

USER: OK, thanks for your information.

ASSISTANT: Thank you, Have a great day.