You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

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

ASSISTANT: Sure, I will help you to change your existing reservation.

USER: Thank you.

ASSISTANT: Sorry, there is no reservation found on your name to change.

USER: It's ok, no problem.

ASSISTANT: Ok.

USER: Thank you for checking.

ASSISTANT: Welcome. Thank you for choosing us.