You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I be your helping hand today? May I know your good name please?

USER: Can you please change existing reservation. I'm Sarah Carter.

ASSISTANT: Sure. please wait for a while, I will check and revert you. Thank you for waiting. We are apologize to inform you, we did not find any reservation with your name.

USER: Thanks for the help.