Different kinds of mistakes require different actions in the viva.
If you find a few typos during your viva preparation you don’t need to go out of your way to mention them to your examiners.
If you find a sentence that doesn’t quite make sense you may need to bring it up if you’re talking about that chapter or topic.
If you discover a paragraph or section that is wrong for some reason, it could definitely help to pre-emptively explain what you really meant.
If your examiners ask you about something and you haven’t noticed it before the viva then you need to think carefully in the moment. That’s all. You need to stop, think and respond.
You need to be prepared to acknowledge all kinds of mistakes in the viva, but you don’t need to build up stress about them. Do what you can in preparation, but spend more time getting ready to talk about everything that isn’t a mistake. The focus in the viva is far more on what is right than what is wrong.
