Hello, I am David Walker.
user
Hello, how can I provide assistance to you?
assistant
I want to change my existing reservation due to postpone of my paper presentation at  Phoenix. Could you please help me with doing this?
user
Sure, please wait for a while.
assistant
Sure.
user
Sorry, there is no reservation found on your name.
assistant
No problem, thank you for the information.
user
Thank you for choosing us, have a good day.
assistant