The steps included said to rinse the mortar and pestle (no soap), let it air dry, and then to crush rice into powder over and over until the rice stays white (gets rid of debris left over from manufacturing). Then it said to mash garlic, then add cumin, salt, and pepper, and grind that together. Then clean it again and let it air dry.
EDIT: This is an example.
https://www.cookly.me/magazine/cooking-guide/how-to-season-mortar-pestle/