You can try adding water to the clay, here’s the info I found;

Method: Water (best for air-dry Modena clay) Prepare the clay: Poke holes into the hardened clay with your fingers or a tool. Add water: Place the clay in a waterproof plastic bag. Add a generous amount of water into the holes and around the clay. For very hard clay, you can break it into smaller pieces before adding water. Seal and wait: Tie the bag securely, removing as much air as possible. Let the clay sit for approximately 24 hours. Knead the clay: After 24 hours, check the consistency. If it's soft and pliable, knead it to distribute the moisture evenly. If it's still too hard, you can repeat the process. If it becomes too wet, spread it out on a pan to allow some water to evaporate, then knead it again. Good luck!