You take a PhD one day at a time. Read, write, test, think and do it all again. Day by day you work through the journey.
You take viva prep one task at a time. Read, write, think, talk: each task brings you closer to the viva.
You take the viva one question at a time. Pause, think, respond, then on to the next point. Each question is an opportunity for you to demonstrate something about your research and yourself.
Step by step, each one bringing you closer to success.