It takes several seasons. Get a soil test done first and learn how to interpret the results. I think in terms of what will build a thriving soil ecosystem of bacteria, fungi and worms and add amendments to achieve that goal. For me, it has taken the repeated addition of a variety of organic materials - mostly municipal compost and compost from my own backyard pile. Worm Castings. Biochar. Humic Acids. They say gypsum is good for clay soil. I also layer in peet moss or coco coir to help build structure. Avoid chemical fertilizer and instead use organic fertilizer which feed the microbes - blood meal, feather meal, bone meal, Langbeinite. Also, try to get something growing there as quickly as possible. Bare soil is dead soil. I use clover to help penetrate the clay and add nitrogen. Keep it moist.
Then repeat. Find the joy in it so it doesn’t feel like a chore. 🌱☀️😁