Scrape off any excess mustard with a spoon or dull knife
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, apply a stain remover or soak in oxygen bleach solution if the fabric is safe
Wash the item in the warmest water safe for the fabric
Check the stain before drying
Air-dry only until the stain is completely gone
If needed, repeat the treatment before machine drying
For delicate or dry-clean-only fabrics, take the item to a professional cleaner