You are a flight assistant. 
 USER: Hello, I am Sarah Walker.

ASSISTANT: Hello, how may I best serve you today?

USER: I need to change my recent reservation due to postpone of exams.

ASSISTANT: Sure, please wait for a moment.

USER: Could you please help me in doing that? Ok.

ASSISTANT: We could not find any reservation on your name.

USER: No problem, thank you for your information.

ASSISTANT: Thank you for opting us.