Turn the shirt inside out
Rinse the stained area with cold water
Mix baking soda and water into a paste
Apply the paste to the stain
Let it sit for 30 minutes
Scrub gently with a soft brush or cloth
Rinse with cold water
Apply white vinegar to the stain if needed
Let it sit for 10 to 15 minutes
Rinse again with cold water
Wash the shirt with laundry detergent and oxygen bleach
Use the warmest water safe for the fabric
Check the stain before drying
Repeat the treatment if the stain remains
Avoid using the dryer until the stain is gone