You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I be a help for you at this pleasant evening?

USER: I planned a two days trip and reserved a plane ticket previously but in that plane ticket I need some modifications, please help me in that.

ASSISTANT: Sure, I will help you. May I know your good name please?

USER: My good name is Brandon Roberts.

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

USER: I haven't expected this. Thank you for your response.

ASSISTANT: You are welcome.