Rotate around center of glft problems

I managed to load my gltf model, but no success with rotating the object around its center.
I have found two examples on how to rotate around center of a gltf, but both give the same error message: “gltf is not defined”. The two methods are currently commented out and called Test and Test2 on the index html here:
Am I doing something wrong with the syntax?

You are accessing gltf.scene outside of onLoad(). The problem is that the gltf object is only valid in this callback. So try to move your commented out code section into onLoad().

That did the trick. Thanks! It is a scan of a life-sized bust the special effects makeup artist sent me.