You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: My name is Katherine Collins. I want to change my existing reservation, could you help me out?

ASSISTANT: Sure, please give me a moment to check.

USER: Sure.

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

USER: That's ok. Thank you for your time.

ASSISTANT: You are welcome.