I believe you're asking about the for SketchUp 2015 (possibly with a reference to "66" meaning a 64-bit version or a specific build).
for creating a long, continuous piece (like a complex skin or organic profile) in SketchUp 2015 curviloft plugin sketchup 2015 66
Why focus on SketchUp 2015? This version was a pivotal release in SketchUp's history. It marked the transition to 64-bit architecture for Windows and, crucially for plugin developers, the upgrade to . I believe you're asking about the for SketchUp
: In SketchUp 2015, navigate to Window > Preferences > Extensions . crucially for plugin developers
: SketchUp will now create a curved surface based on your profile and guide curves.