What are some ways to increase your intelligence, pushing it to the upper bounds of your potential? (Note: I'm not talking about knowledge)

Just read this study
https://www.frontiersin.org/articles/10.3389/fnsys.2018.00045/full
and I got curious. They spoke of complex reasoning training that has worked on healthy people as well (https://www.frontiersin.org/articles/10.3389/fnsys.2014.00069/full), but I couldn't find any exercises for that online.