Turn the shirt inside out
Rub the stain with a dry microfiber cloth or clean sponge
Apply a small amount of white vinegar to the stain
Let it sit for 5 to 10 minutes
Gently rub the area with a soft brush or cloth
Rinse with cold water
Mix baking soda with a little water to make a paste
Apply the paste to the stain
Let it sit for 10 to 15 minutes
Rinse again with cold water
Wash the shirt in cold water with a mild detergent
Avoid using bleach
Air dry the shirt
Repeat if needed before drying completely