You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I already book a flight ticket to Phoenix to attend a meeting with share holders, but due to some reason meeting got postponed. So I want to change my existing reservation.

ASSISTANT: Sure, we are here to help you. Can I have your name to proceed further?

USER: My name is Melissa Brown.

ASSISTANT: Ok, please wait a moment, let me check your reservation in our database and let you know.

USER: Sure, I will wait for your reply.

ASSISTANT: Thank you for your valuable time, unfortunately no reservation found with your name in our database.

USER: Ok, thank you for the information.

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