You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Margaret Lopez.

ASSISTANT: How can I help you?

USER: 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 reservation.

USER: Thank you.

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

USER: That's ok, not an issue. Anyway thank you for checking.

ASSISTANT: Welcome, have a nice day. Thank you for choosing us.

USER: Welcome.