To reroot a Christmas cactus, follow these steps: 1. Gather the materials you'll need, including a pot, soil, water, and a healthy stem from your Christmas cactus. 2. Remove the Christmas cactus from its pot and gently break up the root ball with your fingers or a fork. 3. Rinse off any dirt or debris from the roots. 4. Trim the bottom of the stem with a sharp knife or pruning shears. 5. Fill the pot with a well-draining soil. 6. Dip the trimmed stem into rooting hormone and place it in the soil.