You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. May I know your good name please?

USER: Sure, I am Karen Martinez.

ASSISTANT: How are you doing Mr. Karen?

USER: I am doing well.

ASSISTANT: That's good to hear. How can I assist you?

USER: Because of my health issue I want to change my existing reservation.Can you please help me?

ASSISTANT: OK, don't worry I will help you with that. Please give me a minute so that I can check with your details.

USER: Sure, take your time.

ASSISTANT: Thank you for waiting. Sorry, there is no existing reservation to be changed.

USER: OK, that's fine. Thank you for your information.

ASSISTANT: Thank you for choosing us. Have a nice day.