Hello.
Hello. How may I help you at this moment?
I am Joshua Williams. Could you please help me with changing my existing reservation due to postpone of my exams?
Sure, I am happy to help you with that. Please give me a moment to check it.
Sure, I will wait for your response.
Thank you for waiting, as per your request I have checked in our portal but it is showing that there is no reservation found for the user name in our list.
No worries, I think the  reservation was not done properly.
It might be happened.
Thank you for the information provided.
You are most welcome and thank you for approaching us. Have a nice day.