You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: Sandra Williams here.

ASSISTANT: Sandra, how can I guide you?

USER: I want to change my existing reservation due to my health issue, will help me over that?

ASSISTANT: Sure Sandra, hold on for a moment. I'm sorry, there are no reservations found on your name.

USER: Ok, no problem.

ASSISTANT: Thank you, have a good day.

USER: Thank you for your response.