Rinse the stain with cold water as soon as possible
Blot the area with a clean cloth
Apply a small amount of liquid laundry detergent directly to the stain
Gently rub the fabric together or use a soft brush
Let it sit for 10 to 15 minutes
Rinse again with cold water
Soak the sheets in cold water if the stain remains
Add oxygen bleach to the soak if the fabric is safe for it
Wash the sheets in cold water
Check that the stain is gone before drying
Repeat the treatment if needed
Avoid hot water and machine drying until the stain is fully removed