If one of your examiners doesn’t agree with some aspect of your work that doesn’t automatically mean you fail. It doesn’t mean the outcome of the viva jumps to major corrections. And it doesn’t mean you’ve done anything wrong.
It means that they disagree. They could disagree with a question, an idea, a method that you’ve used, a position that you hold or a conclusion that you’ve reached. It means that you’ll need to talk about it – but you have to talk and discuss your work in the viva whatever topic comes up.
Disagreement does mean you need to listen extra carefully. Ask questions to be certain of what your examiner disagrees with. Respond appropriately. It’s not the end of the world or the end of the viva. Disagreement shows a different perspective in some way. Sometimes you just have to listen and take note.