Read your thesis. Write an overview. Have a mock. Congratulations you did it!
There is a lot of good, general advice for the viva but it can’t be reduced to an easy step-by-step instruction book. The unique nature of every viva, thesis and candidate mean that prep has to be individual.
And still: every submission period of prep work comes down to making time and doing the work. Reflecting, checking, thinking again, getting ready and reminding yourself that you are a good researcher.
Do the research, get your thesis done, do the prep – do all of this and you’ll succeed.
Step-by-step you go towards success.