You take the bowl in which it resides, you clean that with… whatever, soap, shampoo, dishwashing liquid. Use a dish sponge from the rough side, gets the best results 👍. Then, you fill that up with some hot water and pour some soap/shampoo/dishwashing liquid in that and start stirring that with the toilet brush, just grinding it in there. You do that for about a minute, it should be shiny as new.