You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I assist you today?

USER: I am Christine Miller. I want to change my existing reservation as my exam got postponed. Please help me out.

ASSISTANT: Sure, I am here to help you. Sorry Miller, there is no reservation found as per your name to change your reservation.

USER: No issues, thanks for the inforamation.

ASSISTANT: You are welcome.