How to edit STL model files
I think it depends on your use case.
As Bobt already commented, Meshmixer is a common tool for editing STLs.
But also a lot of CAD-Tools should be able to import STLs.
Then there is also of course Blender.
As you didn't specify what you want to use it for, I would guess you just want to do some quick fixes to the mesh.
The tool I use is Meshmixer. It's pretty powerful, but I personally never really used a lot of it's capabilities.