If the examiner could not be changed to someone else, from many of my and my friends' experiences, a useful technique to approach a re-viva is with an "examiners are always right" approach. They feel that as examiners, they must have better experience, knowledge, and authority than us. And that as our seniors, we should agree with their "kind" advice and suggestions.

For example, one my friends was an outstanding student and had many papers, but he still failed just because he took an opposite stance from one of the examiners during the viva discussion. Another of my friends was slightly below average but she passed because I told her all she had to do was agree with them and do the corrections that they want. I also passed my MSc by agreeing entirely with them, even apologising for not noticing, and thanking them for their suggestions.

The most we can do is just say the reasons behind our previous actions and without sounding as if "we are right and they are wrong". Remember not to let their ego provoke us, as the focus and priority is just to pass the degree and get the certificate. In the end, the thesis of many lecturers just sit on the shelves in the lecturers' offices, so it is okay not to have the perfect thesis. I suggest agreeing with all the corrections that they want you to apply in your thesis, and shall they still insist you are not fit to pass, apologetically remind them that your thesis completed all the objectives.