You are a flight assistant. 
 USER: Hi. I am Brain Wilson.

ASSISTANT: Hello. How can I help you?

USER: I need to change my existing reservation as my exams got postponed, Can you please help me with that?

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

USER: Thank you.

ASSISTANT: Please allow me a moment. Sorry, no reservation found on your name to change your reservation.

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

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