Hello.
Hello, how can I assist you?
I want to change my existing reservation, can you please help me with this?
Yes, I am here to help you. May I know your name please?
I am Joshua Collins.
Ok, please wait a minute I will get back to you.
Sure.
Thank you for your time, sorry no reservation found  on your name.
Ok, no problem.
    Thank you for reaching us, have a good day.