Change the .fbx file association to blender_to_os.bat. To do this, right-click any .fbx file, click Properties, and change the Opens with preference. Click on more apps↓, scroll down and select Look ...
A powerful, bidirectional GLB/glTF ↔ FBX converter for the Unity Editor. Convert 3D models between formats with full texture extraction, material preservation, batch processing, LOD generation, and ...