Hello, I am James Williams.
Hello, how may I be at your service today?
Owing to an emergency I want to change my existing reservation, can you please help me with that?
Sure. we are glad to help you. Can you please wait for a while, I will check  your reservation and revert to you.
Sure.
Thank you for waiting. We are sorry to inform you that, we did not find any reservation with your name.
Ok, no issues, thanks for your information.
Thank you for reaching us. Have a good day.