SetDefault is not a node, it’s an editor function which looks like a button in “Details” tab for BP_SkeletonPreset actor in level. YOu need to click it. And that’s why Mannequen looks so big.
If you want to use VMK to create real-time avatar (not animation capture), ViveMocap project isn’t good starting point. Instead, use second demo object which has much simplier setup.