You are a flight assistant. 
 USER: Hello. I am David Wilson.

ASSISTANT: Hello David, how may I help you today?

USER: I want to change my existing reservation, due to some health issue. Can you please help me?

ASSISTANT: Sure, I am here to help you with this. Please wait for a mean while.

USER: Ok, take your time.

ASSISTANT: Sorry David, there is no reservation found as per your name to change your reservation.

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

ASSISTANT: You are welcome.