Fix Holes in Mesh

I am getting this error when I use Solid Inspector2 on my project. It happened after I “subtracted” two groups to cut a hole in a cylinder.
How do I “manually inspect” and repair the “holes in the Mesh” ? I do see some small imperfections in the design when I zoom it up.

Thanks

Very likely the holes occurred because the operation resulted in some very short edge segments. Scale the model up by a factor of 100 or so and then you should be able to work around the bad spots and fix them by drawing in the missing lines. There are some extensions such as Solid Inspector 2 from the Extension Warehouse and TIG’s Solid Solver from Sketchucation that might be able to automatically repair at least some of the issues but fixing them manually can definitely help you learn about geometry in SketchUp.