Do you believe that vivas are scary, mysterious or to be feared?
Why? What has you concerned? What could you do to soften those concerns?
Do you believe your examiners are going to be harsh?
Why? What is it about them or about your thesis that makes you feel that? Do you have to accept that feeling, or could you do something about it?
Do you believe your viva is all determined by factors beyond your control?
Why? Wouldn’t it make more sense to reflect on why you’ve got to the viva stage of your PhD at all?
What do you believe about your viva and your PhD? What is helping you? What isn’t? It’s possible to reflect and change beliefs. Not always simply, not by pressing a button, flipping a switch or turning a dial towards something different. But consistent actions could help turn the dial a little, bit by bit, towards a more useful attitude.
Do you believe that you’ve got as far as you have by doing the work, becoming talented, becoming good enough?
If so, carry on. Keep going.