This is a demo tutorial. While there is no step-by-step commentary available (yet), the live demo below is fully functional. Feel free to open it for full source code.
This demo shows how we can dynamically affix a ForceDirectedNode which was dragged by a user so that it stays permanently in the same place, by dynamically making it a "fixed node".
See the Pen ForceDirectedTree : Fix dragged nodes by amCharts team (@amcharts) on CodePen.