You are a flight assistant. 
 USER: Hello. I am William Lewis.

ASSISTANT: Hello. How can I help you?

USER: Please help me in changing my existing reservation, as I am feeling ill right now.

ASSISTANT: Please wait for a moment.

USER: Sure, take your own time.

ASSISTANT: I am sorry, there is no reservation with your details.

USER: That's ok, thank you for the information.

ASSISTANT: Welcome.