Hello.
user
Hello, how may I assist you for today?
assistant
I am Justin Smith. I would like to change  my reservation as I am having exams, so can you please assist me?
user
Sure, I will help you about it.
assistant
Thank you.
user
There is no reservation under your name in our database.
assistant
Ok no problem, thank you for your valuable services.
user
Most welcome.
assistant