How to clean a stained carpet

I've had good luck using baking soda. I pour a little BS on the stain rub it in, then add a small amount of water. Depending on the texture of the carpet I use a brush or rag to rub the satin out. Clean with a damp rag and vacuum when dry.

I worked baking soda deep into the fibers of the carpet and then sprayed a mix of one part hydrogen peroxide to two parts water on it. I scrubbed with a brush, blotted with a clean cloth, and vaccumed while it was still damp (not wet). My little dog would bring plumbs that fell from the tree into my bedroom to eat them. I got all the stains out with this method, even long after they dried out.

Put vinegar on baking soda instead of water or hydrogen peroxide on instead of water.

If all methods fail - consider having it patched, if you have any carpet, or a piece from a closet.

If none of the stain removers work I have seen someone use wood stain on a carpet to change the entire color of it...

https://cleaning.lovetoknow.com/How_to_Remove_Old_Stains_From_Carpeting

Be aware, that if you are going to dye/stain/paint your carpeting, the stain may take the dye/stain/paint differently than the rest of the carpet and will still show. Please try it on an inconspicuous corner first.

Use 1/4 cup of white vinegar, 1 tbsp. of Dawn dish soap, and fill with water. Spray area liberally and let soak for 5-10 minutes and then proceed with blotting with a clean, dry towel until stain is removed. Some carpet stain removal products can be of great benefit for combating many types of carpet stains.