To fix an ABC 3D model without online tools, use free desktop 3D software like Blender or Meshmixer to repair common issues such as non-manifold edges, holes, or flipped normals.
These tools let you delete duplicate vertices, fill gaps with built-in "Fill Hole" features, or recalculate normals to ensure the model’s surface is consistent, all offline.
For easier repairs, enable Blender’s "3D Printing Toolbox" add-on—it scans for problems and offers one-click fixes, which is helpful for beginners.