Hi, I am Barbara Perez.
user
Hello, How can I help you?
assistant
I want to change my existing reservation.
user
Sure, Please wait for a couple of minutes.
assistant
Sure, I will wait.
user
I will check the existing reservation and revert back to you. Thanks for waiting. Sorry,  There is no reservation found with your name.
assistant
OK, thanks for your information.
user
Thank you, Have a great day.
assistant