How to get rid of mold/ stains from an outdoor carpet?

It might go deeper than carpet. Did you check underneath first. If it's over concrete - then treat concrete and use a mild soap solution to clean carpet.

https://www.wikihow.com/Clean-Artificial-Grass

Where your stain is get a hypodermic needle(where I don't know) - home depot has a premixed solution for mold. Use needle to get solution underneath carpet, but read directions first. Get a fan to blow on carpet where you insert mold solution so you can really get it dry. Once dry clean top of carpet with mild soap solution and again use fan to dry. Should be able to dry fast enough. Hope this helps. Maybe someone else has a different way or I would go to "Pintrest". Look for "diy get rid of mold underneath outdoor carpeting"

Did you get message re using a 💉 to get mold solution under carpet. Use fan to dry real good. Then apply mild soapy solution to clean rug. Again use fan to dry faster then letting it dry naturally.