You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you today?

USER: Can you please help me by changing my existing reservation?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: My name is Dennis Roberts.

ASSISTANT: Sorry Roberts, there is no reservation found as per your name to change your reservation.

USER: Ok, not an issue. Thank you for providing information.

ASSISTANT: You are welcome.