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

ASSISTANT: Hello, how may I assist you today?

USER: My brother marriage got postponed, I need to change my existing reservation. Can you help me for change reservation please?

ASSISTANT: Sure. Please wait a moment, I will check the availability of existing reservation to change it.

USER: Sure.

ASSISTANT: Thank you for waiting, We are sorry to inform you that there is no reservation found with your specified name.

USER: Thanks for your valuable information.

ASSISTANT: Thank you for opting us, Have a nice day ahead.