You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

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

ASSISTANT: Sure, may I know your name for the changing process?

USER: My name is Williams Brown.

ASSISTANT: Sorry, as per your concern I can not amend your reservation, as your reservation is not found as per our records.

USER: That's fine, thank you for your service.

ASSISTANT: Welcome, Thank you for reaching us.