If the paint is still wet, blot excess paint with absorbent paper and rinse article under warm water.
If the stain has dried, place a few sheets of paper towel between the laundry surface and the garment. Soak the stained area with rubbing alcohol. The resins in the paint will be broken down by the rubbing alcohol. With a soft-bristle toothbrush, gently lift the stain from the fabric, going both with and against the grain of the fabric. Repeat until stain has lifted entirely.
If the stain won’t budget, soak the garment overnight in a litre of water with 2 tablespoons of ammonia, 2 tablespoons of white vinegar and 1 tablespoon of salt. The next morning, gently rub with toothbrush once more to finalise the stain lifting process.
Wash in hottest water recommended for the fabric.