Scrape off any excess mustard with a dull knife or spoon
Rinse the stain from the back with cold water
Apply liquid laundry detergent or dish soap directly to the stain
Gently rub the fabric together or use a soft brush
Let it sit for 5 to 10 minutes
Rinse thoroughly with cold water
Repeat if the stain remains
For stubborn stains, soak in cold water with oxygen bleach if the fabric is safe for it
Wash the item according to the care label
Check the stain before drying
Air-dry until the stain is fully gone
If needed, repeat the treatment before using heat