In cases of bleach stains and avoiding patchwork if need be, you might get lucky with this carpet dye system made for bleached carpets specifically : Homeowners Bleach Stain Carpet Repair Kit by bleachstain.
It’s a bit pricey, but has many customer reviews expressing successful use. Please be sure to make sure product is compatible with your specific carpeting before trying it. Bleachstain.com welcomes you to contact them for further details.
If you’re looking for an inexpensive alternative, or a universal option for dyeing any carpet stains, try Rit DyeMore Advanced Liquid Dye for Polyester, Acrylic, Acetate, Nylon and More, or, Rit Dye Liquid Fabric Dye, Black 8 oz
They’re very cost-friendly, offer a variety of colors in order to get blended match needed per your carpet color requirements, and this company also welcomes you reach out for further details.