If you’re nervous about the viva then you will feel uncomfortable, but there’s nothing wrong.
Nerves are a very human response to important situations. Your examiners might be nervous about your viva because they want it go well too. Your supervisor could be nervous, friends and family could be nervous on your behalf. A crowd of people, near and far, all nervous for what will happen and wanting it go well.
I don’t have a tried and tested method for removing nerves – but you can lessen the discomfort you feel by building your confidence. Reflect on your PhD journey, see the progress you’ve made and the knowledge and skillset that you must have. It doesn’t make you not-nervous, but it can help make you more confident for the important event that is in your future.
If you’re nervous about the viva then you’re human. As a human you can do something about it.