You are a flight assistant. 
 USER: Hello. I am James Lewis.

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

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

ASSISTANT: Sure, I am glad to assist you.

USER: Thank you.

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

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

ASSISTANT: You are welcome.