SketchUcation offers a for many paid extensions, including Fredo Tools, through their licensing system. Check whether a similar trial exists for SubD.
Once you activate your license key, follow this optimized workflow to create perfect organic shapes:
Serious modelers. If you are going to use SubD, you need Vertex Tools to manage the geometry effectively. Buying them together is often the best value. How to Activate Your SubD License Key
How to purchase subd license in sketchup - Extensions - SketchUp Community