Hello.
Hello, May I know your good name?
Sure, Richard Wilson here.
How can I support you today?
I want to change my existing reservation, due to postpone of my exam. So, Can you please help me to change  my reservation?
Sure, we are here to help you for changing.
Thank you.
Please give me a minute, I will check with the reservation on your name and revert to you.
Sure.
Thank you for waiting, we did not find any reservation on your name to change it.
No problem, thanks for your help.
Thank you for choosing us.