You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am David Green.

ASSISTANT: David, how can I assist you for today?

USER: Due to some changes in my trip, I want to cancel my recent reservation. Can you help me?

ASSISTANT: Sure, I will help you with that. Sorry David, there is no reservation found on your name.

USER: No problem.

ASSISTANT: Thank you for choosing us, have a nice day.

USER: Thank you for your help.