You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

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

ASSISTANT: I can help you with that.

USER: Thank you.

ASSISTANT: May I know your name to change to the reservation?

USER: My previous reservation is on the name of Daniel Lopez.

ASSISTANT: Ok Lopez, wait a moment please.

USER: Sure, take your time.

ASSISTANT: Sorry to say that, there is no reservation found on your name.

USER: Ok, no problem.

ASSISTANT: Thank you for choosing us.

USER: Thank you for checking.

ASSISTANT: You are welcome.