Improving brain function isn't much different than improving muscle function.
Since our brain is also just a muscle that is specialized on adapting, training it like other muscles works just as well.
This means if you do something or challenge your brain in something for long enough, your brain will adapt to perform better.
Applying this to IQ maxing is simple: just specify exactly what you want to get better at (e.g., reasoning, math, quick thinking, etc.) and then do that repeatedly and to your limit, just like in the gym.
If you want to improve general intelligence, that's most often done by improving reasoning and pattern matching/detecting.
Good luck homie.