>>326077503
normal maps use the color coordinates as normal offsets in tangent space (specifically, mikkt space). I don't know what the best tool to edit them is. krita has a "tangent normal brush" mode that might work for you. if you're okay ditching the current normal map, it's often easier make a copy of your model, use sculpting to make a high-poly/high-detail mesh with whatever detail you want, and bake the normal map instead.