Vivas don’t just happen as some kind of almost-full-stop on the PhD. They’re done for a reason. There are aims of the process. Find out what they are – this isn’t a great secret, explore around on this blog and you’ll find lots of discussion on the topic!
Examiners have aims with their research: topics they’re interested in, questions they want answers to. While the viva is about you and your work, your examiners bring their agendas and ideas. Find out their aims by looking at their recent work. See how that might connect (or not) with your work. Explore how that might impact your viva.
And remember your aims: you had them. Maybe they changed, perhaps in some cases they were unfulfilled, but you had them. What started you off on the process and where did it lead you? How important are those aims for the conclusions of your thesis?
And how could you communicate that if asked in the viva?