Set Your Intention
You intend to pass your viva! So what will you do?
You intend to submit the best thesis you can! So what will you do?
You intend to respond as well as you can in the viva! So what will you do?
Intention helps. Actions follow intentions. You can set a goal and hope or you can decide what steps you will take. The latter is probably more effective!
If you intend to prepare well then perhaps make a plan for your viva prep. Leave room for the unexpected. Make good time for you to do it when you won’t be stressed or tired.
If you intend to engage well in the viva then rehearse. Have a mock viva. Talk with friends. Read your thesis. Do a lot of thinking.
If you intend to pass your viva then don’t just hope that it all goes well. Make it certain.