You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello. How can I assist you?

USER: Please change my existing reservation.

ASSISTANT: Ok, surely I will help you. Please wait a moment. Ok, please provide me your name.

USER: My name is Sandra Lewis.

ASSISTANT: Sorry Sandra Lewis, there is no reservation been found on your name.

USER: Thanks.

ASSISTANT: Thank you for choosing our agency. Hope you will connect again next time.