Where will your viva take place? You’ll know in advance. Examiners don’t surprise candidates on the day with the examination room.
Since you’ll know before the big day, go and check it out. What is the space like? Are there any distractions you have to think about? Is there a whiteboard if you need one? Can you sit with your back to the clock? People feel comfortable in some spaces, and less so in others. What can you do to encourage the thought that the venue for your viva is good for you?
Remember that your viva really takes place in the discussion. So reflect: what can you do to make that space as comfortable as possible for you?