You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

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

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

USER: Thank you.

ASSISTANT: Give me a moment. May I know your name?

USER: Myself Dorothy Rodriguez.

ASSISTANT: Sorry, there is no reservation is found in our data base to change your existing reservation.

USER: No problem, thank you for checking.

ASSISTANT: Welcome.