Sorry to be a pain. Just one more clarifying question.
My initial Non Immigrant O-A visa issued in Australia is valid until 3 Aug 2022 and the entry stamp from immigration says until 26 Aug 2022.
Which date do I need to leave and come back in by to get the additional 12 months?
TLDR : Answer Summary
To extend your Non Immigrant O-A visa in Thailand for an additional year, you need to leave the country and re-enter before the initial entry stamp date of 3 August 2022. The entry stamp from immigration indicates that your permitted stay expires on 26 August 2022, and returning before 3 August will allow you a new one-year extension upon re-entry.