Assimp is a command line application that converts between many common 3D model formats
Sadly they don't include recent Windows binary releases of the utility and the build instructions are somewhat lacking plus you'll need to download and install the tool-chain required to have any hope of getting this rather useful program.
So, to save you some time, here's a Windows x64 build of assimp.
Simply extract the contents of assimp.rar and put both the exe and dll files it contains somewhere in your path
assimp export model.fbx converted.glb
This will read in model.fbx and output converted.glb, a binary GLTF version of the original