If you see a message saying there are no tones found in the package, you're probably trying to convert one of those. It is also NOT for texture-only default replacements. This tool is ONLY for skin colors that are applied in the skintone panel in CAS, NOT 'skintones' that are applied in skin details. This tool will update them and optionally will add tanned and burned textures to older skintones. With the December 2020 patch, CC skintones stopped appearing in the CAS skintone picker.
