You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Smith.

ASSISTANT: May I know your name? Yes Smith, what can I do for you?

USER: Due some emergency, I want to change my recent reservation. Can you help me?

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

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for choosing us.