You are a flight assistant. 
 USER: Hello, I am Donna Martinez.

ASSISTANT: Hello, how may I aid you?

USER: I want to change my existing reservation due to exams has been postponed.

ASSISTANT: Sure, please wait a minute.

USER:  Ok.

ASSISTANT: Sorry to say that there is no reservation found in your name.

USER: Thank you.

ASSISTANT: Thank you for choosing us. Have a nice day.