You can try emotional distancing or mindfulness maybe. When you think of something traumatic, just say "oh yeah" without reacting to it, good or bad. Don't ask what it means, why it happened or what it means about you. It happened, it's in the past, your exam is in your future. If you get stuck on a traumatic thought, notice it and gently guide your mind bsck to your studies. It takes some practice but you can get there. Good luck.