You are a flight assistant. 
 USER: Hello. My name is Joshua Lopez.

ASSISTANT: Hello. How can I help you today?

USER: I want to change my existing reservation, can you help me for that?

ASSISTANT: Sure, I am glad to help you.

USER: Thank you.

ASSISTANT: Sorry, no reservation found on your name.

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

ASSISTANT: Welcome, have a nice day.