If you don’t clean the stain right away or you wash it in hot water, blood can absorb deep into a fabric’s fibers, creating a set-in stain that’s difficult to get out. If that happens, try spraying the underwear with an enzymatic cleaner, which is designed to break down the enzymes in biological stains, like blood. Let it sit according to the label’s directions, then wash your underwear in cold water.   You can typically find enzymatic cleaners at major retailers that sell cleaning supplies, but if there isn’t one available near you, you can order them online. Oxygenated bleach may also help remove set-in stains. If you don’t have these products available, you might be able to remove the stain with items you already have at home, like baking soda, lemons, or meat tenderizer. Mix about 1/4 cup (45 g) of baking soda with 1  tsp (4.9 mL) of water at a time until it forms a thick paste. Then, spread that paste over the crotch of your underwear so it completely covers the stain. Leave the baking soda in place for at least 30 minutes, but for the best results, let it sit overnight. Afterward, wash and dry your underwear as usual. You can also make a paste from unseasoned meat tenderizer or crushed aspirin or ibuprofen tablets. Cut a lemon in half, then rub the cut side of the lemon over the bloodstain on your underwear. Continue doing this for about 3-5 minutes or until you see that the stain is gone, then wash your underwear in cool or cold water and hang them to dry. Do not use this on brightly-colored or dark underwear, as the lemon juice will stain them.

How would you rephrase that briefly using Chinese?
喷洒含酶清洁剂，去除已经凝固的顽固血迹。 用小苏打膏覆盖血迹，温和地去除它们。 用柠檬汁漂白浅色内裤。