You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

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

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

USER: Thank you for accepting my request.

ASSISTANT: Please allow me a moment.

USER: Ok, take your time.

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

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

ASSISTANT: Welcome, have a nice day.