You don’t get a PhD by just showing up. There are no shortcuts, no study hacks, no “five simple tricks” to help you dodge the work you have to do.
A PhD is a result of time, work and talent. Maybe a little luck will help, but it’s not the deciding factor. A PhD is hard. The viva is part of the PhD, so you can’t expect it to be easy.
But don’t expect it to be too hard either. It’s not trivial, but it comes after all of the other hard PhD days you’ve lived through.