Hi,.
Hello,. May I know your name?
I am Matthew Smith.
How can I aid you?
I want to change my existing reservation due to my friend's birthday party place has been changed. Can you help me in doing this?
Sure, I will assist you.
Thank you.
Please wait a while let me check and let you know you the status.
Sure.
Thank you for your time,  I have checked in reservation list to change your existing reservation details, but could not find any reservation with your name.
Ok, no issues. Thanks for your kind response.
Thank you for availing us. Have a nice day.