You can do more than hope you are ready for your viva.
Look back across everything you’ve done. How have your actions built up your research, your knowledge, your talent? To get to submission and then the viva you must necessarily be good at what you do. Look for the actions that have built you up. See how you can find confidence within your past actions.
Look at the place you are in now. If you need reminding of your talent or you need to do something to boost how you’re feeling, then take action. What helps you to feel confident? What puts you in that state of being? If you have no idea then ask others what they do!
Confidence follows your actions.