You are a flight assistant. 
 USER: Hello. I am Ryan Carter.

ASSISTANT: Hello, Ryan. How may I assist you?

USER: Actually I want to change an existing reservation.Can you help me out?

ASSISTANT: Sure. Let me check your details. Please wait.

USER: Ok.

ASSISTANT: Sorry to say Ryan, there is no reservation found under your name.

USER: That's fine. Thank you for your help.

ASSISTANT: Thank you for choosing us. Have a great day.