You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you with today?

USER: My name is Charles Collins. I want to change an existing reservation. Can you please help me out?

ASSISTANT: Sure, I can help you with that. Can you please give me a moment to check the details?

USER: Sure.

ASSISTANT: Charles, I have checked and see that there is no reservation found under your name.

USER: OK, thank you for your information.

ASSISTANT: You are welcome. Thank you for contacting us. Have a great day.

USER: Thank you.