Make a list of potential questions that you could be asked in the viva. I did some of this as I was writing my thesis, as inevitably you have to summarise or cut parts that are too long, so these are ripe topics for questions. I also made use of lists of viva questions that other people have prepared; a particularly extensive and useful example is at the end of this blog post: http://salmapatel.co.uk/academia/phd-viva-preparation-steps/.
Practice answering these questions out loud. Get someone to quiz you if you can. Especially practice the length of your answers -- don't just say yes or no, but don't waffle for five minutes either. Focus on answers to "soft" questions such as "tell us about your thesis", as they'll likely start the viva with something along those lines and it will relax you if you can answer that confidently and smoothly.
Summarise your thesis. I made notes on the key points/arguments of each chapter, as well as noting any key figures or tables that I might need to refer to. Since your viva is on Zoom, you can even add bookmarks and annotations to your pdf document, and have that open on your computer while the viva is ongoing (I did this, but in the end didn't refer to a single one).
Re-read key papers. I identified about fifteen key papers in the literature that my research was based on, or whose methodologies I had followed, or had key results that mine agreed/disagreed with. I made sure I knew the main points of all these papers and how they related to my work. I think this was the most valuable piece of preparation I did, as it made me very confident that I knew the literature, and I answered some questions in the viva very well by explicitly referring to these key works.
Have a mock viva. You can ask your supervisor to arrange this. It doesn't have to be as long as the real thing (mine was about an hour). It's a chance for you to get familiar with the set up (although we're probably all old hands at Zoom by now), and practice answering some of the more general questions. This really helped relax me and demystify the process. Make sure to arrange it about a week before the real thing, so you have time to act on any suggestions they might have.
Don't over-prepare! You know your own work better than you think. I was so worried that I needed to revise all of undergraduate physics and the background to every topic in cosmology, but in reality theythe examiners asked me very few questions that didn't directly relate to my research. It was also fine when I said "I don't know" (which happened quite a lot!); they guided me through an answer and seemed happy to hear my reasoning.
Other observations: the external examiner asked me the more "nit picky" questions, while the internal asked basically the same questions for each chapter: "tell me about this chapter", "what was your contribution?" for chapters based on multi-author papers and "choose a result or figure from this chapter and explain it to me". You will probably have an independent chair in the meeting too, though they will stay silent throughout unless there is a problem. The Zoom viva will probably be shorter than if it was in real life -- mine was barely over two hours and I left almost disappointed that it wasn't longer!
A great answer about what to expect in a viva and how to answer those "soft questions" is here: https://academia.stackexchange.com/a/59811/49043.