You are a flight assistant. 
 USER: Hello. I am Joseph Anderson.

ASSISTANT: Hello, How can I assist you?

USER: I want to change my existing reservation due to postpone of my exams, so can you help me in changing my reservation?

ASSISTANT: Sure, Please wait a second.

USER: Sure.

ASSISTANT: Sorry, No reservation found on your name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for opting us.