Select the file first and click Open. Confirm any security prompts. Repeat the process for the Curviloft .rbz file.
In 2015, SketchUp still used the legacy OpenGL renderer. Heavy geometry slowed down drastically. Curviloft was optimized to produce that could be softened and smoothed. This balance—organic shapes with efficient geometry—is why professionals clung to this version. curviloft plugin sketchup 2015 66