If you feel nervous before your viva there is typically a simple explanation: you’re recognising that the viva is important.
You need to pass, you’ve invested a lot of work to this point, and even though the vast majority of candidates pass, there’s still that little quiet voice saying, “Come on, you’ve got to do this!”
You will. It’s important, so you feel nervous. You can choose what you put your attention on. Let your actions focus on doing the viva well, rather than on beating away your nerves.