You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you?

USER: Please help me in changing of my existing reservation.

ASSISTANT: Sure, I am here to help you out.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Anna Thomas.

ASSISTANT: Wait a moment please.

USER: Ok.

ASSISTANT: Anna Thomas, we haven't found any reservation under your name in our database.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for choosing us.