You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Ronald Allen.

ASSISTANT: Good evening Allen.

USER: Due to my health problem I want to change my existing reservation.Can you please help me out?

ASSISTANT: Sure, I will help you. Please give me a minute.

USER: Sure, take your own time.

ASSISTANT: Ronald, there is no reservation found with your details.

USER: That's fine. Thank you for your help.

ASSISTANT: Thank you for choosing us, have a good day.