The stain remover OxiClean is good at removing stains that are fresh but when stains get old and set in the clothes or laundry then even OxiClean has a hard time removing those old set in stains.
Sometimes OxiClean will remove old set in stains if you put some OxiClean in a bucket of warm water and then allow the laundry to soak in that warm water and OxiClean mixture overnight.
Agitate the laundry in the bucket of OxiClean and water to help mix the OxiClean and water together and also scrub the clothes together where the stain is.
Sometimes doing that will allow the OxiClean to remove the old set in stain depending on how old the stain is and what is actually staining the clothes.
Sometimes you may need to soak the stain in some vinegar and baking soda and warm water.
Or pour some baking soda on the old stain and then pour some vinegar onto the stain and allow it to sit for 30 minutes and then scrub the stain with a toothbrush.
You may also need to use a commercially made stain remover to remove the stain.
Older stains are harder to remove than fresher stains so it's best to remove stains as soon as they stain the clothes.