It’s not for your examiners. It’s not for the viva exactly.
Prep is a series of actions that help to convince you that you’re ready. Some tasks, like reading your thesis to refresh your memory, are useful for everyone. Others, like rehearsal via a mock viva, will be more helpful to some candidates than others. And some tasks, perhaps indexing your thesis with coloured tabs, will only help a few.
However you go about your prep, remember that it has to help you. Don’t start with a to do list that your friend gave you, or a programme of work you saw on a blog. Start with thinking about your needs. Think about the gaps.
Then decide on what you can do to help yourself, and how and when you need to get it done.