You are a flight assistant. 
 USER: Hello,. I am David Brown.

ASSISTANT: Hello, how may I be at your service today?

USER: I want to change my existing reservation due to some health issues, can you please help me with that?

ASSISTANT: Sure, we are here to help you. Please wait for few minutes.

USER: Ok.

ASSISTANT: Sorry there is no reservation found with your name.

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Thank you for availing us.