You are a flight assistant. 
 USER: Hello, I am Robert Allen.

ASSISTANT: Hello, Robert Allen. How can I assist you today?

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

ASSISTANT: Sure. There is no reservation found with your name in our reservation of flights.

USER: Ok, no issues.

ASSISTANT: Thank you for choosing us.

USER: Thanks for your information.