The viva’s not the first time you’ve responded to questions about your work.
It’s not the first time in your PhD journey you’ve been tested.
You have to have risen to challenges many, many times to get to submission.
And your viva is not the first ever viva! Lots of people around you – and people who you don’t know on the internet – have experiences that can help you unpick what to do and how you could feel about your upcoming viva.
Again and again you’ve worked hard to get to this stage of your PhD. A little more will help you finish.