Soak overnight with Wisk laundry detergent or dawn, painted just on the stain. Both remove grease. Launder and hang to dry to see if all of the grease has been removed. if not repeat. If you put it in the dryer you can set the stain and make it harder to fully remove.
Dawn and baking soda mixed into a paste and applied to the oil stain will absorb the oil. Let the paste set for a 1/2 hour or so then wash it out and rinse well. You may need to repeat if the stain isn't fully removed.
Dawn should work as Janice suggests. I would squirt some Dawn on the stain and hand rub it into the stain. Then launder as usual. You can also try WD40. Spray the stain with WD40 let it soak in then launder as usual.
I use GoofOff and Dawn. Saturate the stain with GoofOff and then brush with Dawn. Let it sit overnight then was as usual. If the stain doesn't come out using this method, it will never come out.
Hi Mli: Here's a site I found for you that might help: https://www.lalalisette.com/removing-set-in-oil-stains/3/ Good luck
I use plain white chalk. Rub it on the inside of garment and let sit an hour. Repeat if it’s a large spot a few hours and then wash. It hasn’t done me wrong yet. Good luck