Log into the VRChat site, go to downloads, and get the latest copy of the SDK. Check what version of Unity should be used and use it.
Assets > Import Package > Custom package...
VRM0 > Import the VRM
Assets > Import new asset... the FBX (maybe we don’t really need the fbx)
Select the FBX
Rig section: set Animation Type to Humanoid, Apply...
Configure... button under Avatar Definition: Head section, Jaw will most likely need set to none. Verify other bones are correct. Apply, Done.
Materials section: copy the VRM materials to the appropriate Remapped Materials slot if needed. Apply.
Stick the VRM in the scene.
VRM0 > Duplicate and Converter for VRChat
Combine Meshes checked
Swaying Objects: Convert VRM Spring Bones Only (don’t need coliders)
Select the outputted avatar, a few things to adjust in the VRC Avatar Descriptor: