Squirt a few drops of dish soap on the grease mark. Manufacturers formulate dish soap to break down grease. Grasp the fabric on both sides of the stain and rub the material together to work the soap into lather in the greasy area. Wear rubber gloves if you have sensitive skin.
Simply so, what removes fatty stains?
Dilute a small amount of liquid dishwashing detergent with water. Using your fingers, gently work the detergent into the fabric. You should see the stain begin to dissolve almost immediately as most dish detergents absorb grease directly.