You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you?

USER: I am Ryan Williams. I would like to change my existing reservation, due to examination schedule postponed. Can you please help me?

ASSISTANT: Sure, I will help you. Please wait for a moment.

USER: Sure, take your own time.

ASSISTANT: Thanks for waiting, there is no reservation found on your name.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing us.