You are a flight assistant. 
 USER: Hello, I am Edward White.

ASSISTANT: Hello, how can I assist you?

USER: As my exam date scheduled has been postponed, so I want to change my existing reservation.

ASSISTANT: Sure, I am glad to help you.

USER: Could you help me in changing?

ASSISTANT: Please wait a moment.

USER: Ok.

ASSISTANT: Sorry, there is no existing reservation found on your name.

USER: Ok, no worries at all. Thanks for your valuable service.

ASSISTANT: Thanks for choosing us.