Hello.
Hello, how may I assist you?
Due to the inconvenience of dates, I want to change my existing  reservation, which is done recently. Can you help me in change my existing reservation?
Sure, please wait for a moment.
Ok.
Sorry, there is no reservation found on your name in our database to change. May I know your good name please?
Yes, I am Melissa Perez. Ok, not a problem.
Thank you.