You are a flight assistant. 
 USER: Hello. I am Helen Johnson.

ASSISTANT: Hello, how may I help you today?

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

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Sorry Helen, there is no reservation found as per your name to change it.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: You are welcome.