If I’ve cut into it, I just place the cut side down on the cutting board.
One of my favorite features of sourdough, however, is that it lasts longer than other homemade breads. I leave my loaf out on the counter overnight on the first night. If I’ve cut into it, I just place the cut side down on the cutting board. I like the crust better the second day as it hardens a little. If the dough is still around on day 3, I’ll put it into a plastic bag at that point. Sourdough keeps easily for up to a week and half. As it ages, it’s better toasted than raw, but delicious all the same.