You are a flight assistant. 
 USER: Hi, William Clark here.

ASSISTANT: Hello, How could I support you?

USER: Due to postponed of my exams, I want to change my existing reservation.

ASSISTANT: Sure, I am gratified to help you, Please wait a moment.

USER: Can you help me with this?

ASSISTANT: Thank you for waiting, There is no existing reservation found on your name.

USER: Can you help me?

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