You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: I am Ronald Hill. I am planning to change an existing reservation, due to health issue.

ASSISTANT: I understand your request and will be happy to help you.

USER: Can you please change my reservation? Thank you.

ASSISTANT: Sorry, there is no reservation matching with your name in our portal to make changes further.

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

ASSISTANT: My pleasure. If any questions arise, please feel free to contact us at any time.