You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Jeffrey Jackson.

ASSISTANT: How can I guide you today?

USER: I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Sorry, no reservation found on your name.

USER: That's fine. Thank you for your service.

ASSISTANT: Welcome, have a nice day.