You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, may I know your name?

USER: Paul Williams.

ASSISTANT: Thank you. Please wait for a while, let me check your reservation status in our database.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found under your name in our database.

USER: That's ok, no problem. Thank you.

ASSISTANT: You are welcome and thank you for choosing us.