A muriatic acid based cleaner is what you’re looking for I believe. Make sure you read about safe use because, obviously, it’s an acid and a pretty strong one at that.

Should be available at your local hardware store as well.

Good luck!

I got a week-old motor oil stain out of new concrete with some oxyclean and some water—may wanna try that if you already have some on hand.

Find a contractor supply company or Ready Mix concrete producer they have a lot of products for cleaning concrete.

If it's oil type of stains Mineral Spirits works well if it's other type of grim get a professional product and follow the directions to a T.

Google plywood stains on concrete and you'll get a lot of hits. I found this in the first one: "Extracts from wood may cause yellow or brown stains in concrete. The stains can be removed by treating the concrete with a hypochlorite solution. Household bleach, which is usually about 5 percent sodium hypochlorite, is satisfactory after diluting one part of bleach with four to six parts of water. The stain disappears if the surface is first scrubbed thoroughly with a solution that is one part glycerol in four parts water. Glycerol is flammable and bleach is corrosive to skin. As always, read the warning labels on the chemicals before use."

Leave it be, it’ll weather

I thought you were talking about "stained concrete" not concrete with stains. I stained my own floors with an acid stain.

It will naturally be gone in 6 months