You had to ask original questions to find the original contribution in your thesis. You had to do something new and different. What was it? What did you ask that was new? What were the answers or ideas that you found?
Now, to make the viva happen, your examiners might have to invent more new questions. Predicting viva questions isn’t simple or easy, but finding people who can ask you new questions, questions you’ve not been asked before, can be useful. Get your supervisors and colleagues to ask you questions so you can practise responding.
You built your contribution on new questions. Now cement your confidence with them too.