You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you today?

USER: I am Margaret Carter.

ASSISTANT: Yes Carter.

USER: I want to change my existing reservation, can you please help me for that?

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

USER: That's ok, no problem.

ASSISTANT: Thank you for choosing us.

USER: Thank you for checking. Welcome.