If you mean using baking soda to remove very dark stains, it can work for some household stains, but the right method depends heavily on the surface.
For a general household stain
Mix baking soda with a little water into a soft paste.
Apply gently for a few minutes.
Wipe away with a damp cloth and dry.
Test an inconspicuous area first.
⚠️ Don’t use it blindly
Baking soda is mildly abrasive and can damage or dull polished wood, delicate finishes, natural stone, and some fabrics. Don’t mix it with bleach or other cleaning chemicals.
If you tell me what the dark stain is on—wood, clothing, carpet, teeth, grout, skin, etc.—I can give you the safest specific method.
