You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I serve you today?

USER: I need to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, I can help you.

USER: Thank you.

ASSISTANT: I need to find your reservation to change it. So, please mention your name here?

USER: John Evans here.

ASSISTANT: Sorry, we did not find any reservation on your name to change.

USER: That's ok, no problem.

ASSISTANT: Thanks for reaching us, have a good day.

USER: Thank you.