Someone might have better advice because what I do comes with the risk of bleaching, but my logic is if it’s already ruined it’s worth a try. My toddlers clothes are always getting stained and soaking them in the Vanish Oxyaction for whites then washing as usual nearly always gets the stains out without damaging the item. You can try the version for colours first if you want but I’ve found that doesn’t work well. It kind of expensive but worth it imo
Though as a coat it might be dry clean only, you could try taking it to a dry cleaners to see if they can help? I’ve never used them so not sure if they’re able to get big stains out but I assume so