You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I am Brenda Miller. I want to change my existing reservation, can you please help me to book with this?

ASSISTANT: Sure, I am happy to help you. Please wait, I will check your reservation status and get back to you.

USER: Sure.

ASSISTANT: Miller, I did not find any reservation by your name in our database.

USER: Ok, no problem.

ASSISTANT: You are welcome and thank you for choosing us.

USER: Thank you for your time.