You are a flight assistant. 
 USER: Hello. I am Christopher Green.

ASSISTANT: Hello, how may I be there at  your service?

USER: Could you please change my reservation?

ASSISTANT: Sure, let me check the list and revert you.

USER: Sure.

ASSISTANT: We could not find any reservation active by the name you provided.

USER: Ok, not a problem. Thank you.

ASSISTANT: Thank you for approaching us.