Take a solved problem from your new PDF. Erase the final 3 lines of the solution. Can you derive them? Then erase the final 6 lines. Keep going until you are re-deriving the entire solution from the first principle. This builds the "Russian muscle memory."
The official website (reg.olimpiada.ru) archives the latest theoretical and experimental rounds. While the interface is in Russian, you can use browser translation to navigate to "Архив заданий" (Archive of tasks). Here you will find genuinely new problems from the current academic year in PDF format. Look for the files labeled "9 класс" (Grade 9), "10 класс," or "11 класс."
Attempt a problem for 3 days (2 hours per day) without looking at the solution. Russian problems are designed to be insoluble in 30 minutes. You must wrestle with the physics, draw 10 different diagrams, and re-read the problem text 20 times.