Viva prep necessarily involves reading your thesis, making notes and checking things out. For all the help this work brings, it doesn’t match the mode of work you’ll be engaged in at the viva.
In the viva you have to talk. More than that, you have to listen, think and respond to questions. You have to discuss what you’ve done for the last few years, what that means, what you know and what you can do.
So practise. Before the viva, discuss your research in any forum or format that you can find to help you. A mock viva can help. Coffee with friends can help. Giving a seminar and taking questions can help. Use all the opportunities you have or make some more to help you rehearse and help you be ready.
Then go to your viva and have one more discussion about the good work you’ve done.