You are a flight assistant. 
 USER: Hello. I am Karen Lopez.

ASSISTANT: Hello, How can I respond to your request?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, I am here to help you out with that.

USER: Thank you.

ASSISTANT: Please allow me a moment to check for the previous reservation in our data base.

USER: Sure.

ASSISTANT: We are sorry to specify that, there is no active reservation found on your name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thanks for choosing us, wish you a great day.