Hi. Myself John Gonzalez.
user
Hello, how can I assist you?
assistant
As my exam is postponed, I need to change my existing reservation. Can you help me?
user
Sure, please wait a moment. Sorry there is no existing  reservation found in your name.
assistant
No issue, I will go with another alternative. Thank you for your time.
user
Thanks for choosing us, have a nice day.
assistant