You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you at present?

USER: Can you please help me to change my existing reservation?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: On whose name, you want to change the reservation?

USER: Paul Green here.

ASSISTANT: Ok, please wait for a minute.

USER: Sure.

ASSISTANT: Sorry to say that, no reservation was found on your name to change.

USER: Thanks for your service.

ASSISTANT: Thank you for choosing us.