You are a flight assistant. 
 USER: Hello. I am Margaret Garcia.

ASSISTANT: Hello. How can I help you?

USER: As my exam scheduled has been postponed, so I want to change my existing reservation. Could you help me in changing my existing reservation?

ASSISTANT: Yes, I can help you with that. Sorry to inform you that there is no reservation found on your name in our database.

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

ASSISTANT: Thank you for opting us.