Scrape off 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
Wash the item in the hottest water safe for the fabric
Check that the stain is gone before drying
Air-dry if any stain remains
For non-washable fabrics, blot with cold water and use a stain remover suitable for the material