You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I serve you today?

USER: I am Mark Adams. 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. Sorry, there is no reservation found on your name in our database.

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

ASSISTANT: Thank you for opting us.