Put your head over a sink or stand in the shower. Make sure you rinse out the paste completely, as this will help the Vitamin C strip the color out of your hair. If you notice your hair feels dry once you rinse out the paste, you can massage in moisturizing conditioner to give it a bit more moisture. This can also be a good precautionary measure if your hair tends to get frizzy when you dry it, especially when it is dyed. If you usually use a blow dryer to dry your hair, use it to dry your hair so you can assess how light the dye faded due to the paste. If you prefer to let your hair air dry, let it hang loose for several hours or overnight. If you blow dry your hair, use a heat protectant product to limit heat damage. You can apply the Vitamin C paste again if you want to lighten your hair further. It is safe to apply it 3-4 times in a row to lighten your hair, though the paste may dry out your hair and cause your scalp to flake or itch. Always follow up the paste with a moisturizing conditioner if you are using it multiple times in a row to protect your hair and scalp. You can also try leaving the paste on your hair for longer than 2 hours at a time, though this can cause irritation if your have a sensitive scalp.

TL;DR in Vietnamese:
Xả tóc với nước ít nhất 5 phút. Thoa dầu xả lên tóc nếu tóc khô hoặc cứng. Làm khô tóc. Lặp lại quy trình này nếu bạn vẫn muốn tóc nhuộm có màu sáng hơn. Hoàn tất.