To repair a 3D model for 3D printing, use specialized software to fix common geometry issues like non-manifold edges, holes, or inverted normals—critical for printability.
Tools like Meshmixer, Blender, or slicers (e.g., Cura, PrusaSlicer) offer automatic or manual fixes: fill gaps, merge unconnected edges, or flip normals to make the model watertight (required for slicing into printable layers).
For beginners, start with your slicer’s built-in automatic repair; for complex issues, use Meshmixer’s “Make Solid” or “Repair” tools—no advanced skills needed.