You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I guide you today?

USER: My name is Robert Hernandez. I want to change my existing reservation. can you 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.

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

ASSISTANT: Welcome, have a nice day.