You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: I am Samuel Brown. I want change my reservation, please help me in that?

ASSISTANT: Sure Brown, I will help you to change your reservation.

USER: Thanks.

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

USER: That's ok.

ASSISTANT: Thank you for choosing us.

USER: Thanks for helping me.