You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I want to change an existing reservation. Can you please help me out?

ASSISTANT: How may I help you? Can I know your name to check the details?

USER: Sure, my name is Janet Perez.

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

USER: OK, thank you for your information.

ASSISTANT: Have a nice day.