A small part of viva prep is to make sure you have a little familiarity with your examiners’ work.
You might read that and think, “Of course I know about my examiners! I cited them ten times!” That’s not always the case. It may be that your examiners have been chosen for other reasons. Perhaps they are in the same field but you didn’t need to know about their work to do your research.
As you prepare, make sure you know about their work. Just a little. Look at their last two or three papers. Get a sense of what they do, what they know and what they have focused on recently as researchers.
In particular, look for connections between their work and yours. What are the common methods? What are the common themes or interests? When you reflect more on this, what is it likely that they would be familiar with as they come to read your thesis? Is there anything you need to know more about them and their work to feel ready for your viva?
You don’t need to be an expert in your examiners and their research. A little work to explore the connections between you and them will be enough to help you be ready for your viva.