You’re not the first person to feel nervous, excited, unprepared or whatever you feel before your viva. Ask around, find out how others coped.
You’re not the only person in your viva who might feel nervous, wanting to do a good job. Remember that your examiners also want the viva to go well. And you’re not the only person in your viva who will be prepared. You prepare because you want to pass; your examiners prepare because it’s the right thing to do, to show up ready to examine you.
You’re not the only person who will have felt uncertain during the viva before – so again, ask your friends about what their vivas were like, what they did when they felt unsure.
And you’re not the only person who will feel thrilled when you pass, so consider how you can celebrate your success when you’ve finished.