Make a plan for submission. Set milestones to help keep you on track. Check the details for the official things you need to do. Maybe ask a friend to go with you if you have to submit paper copies and make an event of the occasion.
Make a plan for your prep. It doesn’t take a lot to get ready; if you’re already busy it helps to map out what you will do and when you will do it. Ask for help in advance so you can arrange specific times. Start soon enough so you don’t have to rush to finish.
Make a plan for the viva. Think about how you would like it to go, how you would like to present yourself, what you will need for the day. Plan your outfit and supplies. Plan your space if your viva is over video. Decide on how you will try to engage with questions. Check the details but remember that you can’t control everything: you can plan to do your best.
Make a plan for the short break at the end of the viva. Find something to do in that brief period of waiting to occupy yourself.
Finally, make a plan to celebrate your success!