How to plant root bound plants:
Make numerous downward cuts so that the circular roots are cut. This forces the roots to grow outward when they are replanted. Remove any brown or black roots, which are most likely dead. Keep the white roots, which are alive. ‘Massage’ the root ball of your plant, which will help loosen the roots even more.
Plant your plant and its ‘freed roots’ in a larger pot or in the ground. The newly cut roots will grow outward and your plant will start growing again. And that’s all there is to fixing a root-bound plant.