Gather what you need: thesis, notes, pen, paper… What else do you need for your viva?
Decide on what you will wear: wear something for comfort, for confidence, to feel right or to feel happy… Decide in advance to remove a decision from the day of the viva.
Check the details: whether online or in-person, check what you’ll do or where you’ll go… Then put it away for the next day.
Talk if you need to: find a trusted person, someone who can listen if you have any worries or concerns from nerves… You may or may not need this, but find someone in advance who could support you.
Rest: take a break, relax, distract yourself… All the work you can do to get ready has probably been done.