Hi, I am Gregory Walker.
Hello, Gregory Walker. How can I assist you today?
Owing an emergency I had to request  change an existing reservation. Can you help me out with this?
Sure, I am here to help you. Please, wait a minute I will check and revert you.
Sure.
Sorry, I found no reservation in your given details.
Ok, thanks for your information.
Thank you, for opting us. Have a nice day.