You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I be a help for you?

USER: My name is Nicholas Harris. I need your help in changing my existing reservation.

ASSISTANT: Sure, it's my pleasure to help you.

USER: I need my ticket price range should not exceed 500.

ASSISTANT: Sorry, no reservation is available for you. Thank you.Have a great day.

USER: It's OK. Thank you.