Confidence is essential for the viva, but you can’t just turn it on.
You have to nurture it.
If you want to grow vegetables, you could throw some seeds in a hole in the ground and wait to see what happens.
Or you could match the right seed to the right type of soil at the right time of year. Be deliberate. You could track when you water or add nutrients. You could decide how you will trim leaves or not, what supports you might need to help the plant grow well, whether or not you need to do something to help remove pests. There’s a lot you could do to help. You can’t guarantee the outcome, can’t see exactly what the final harvest will be, but you can do your best to steer the situation to the best possible outcome.
You can do the same thing for your confidence in general, and in particular for your viva. You can try things, find opportunities to give you more experience. You can reflect on your progress through your PhD to see times when you’ve clearly improved. You can think about what you could do to help your confidence on the day itself.
Not guaranteeing an outcome, but steering your confidence – and yourself – to the best possible outcome.