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 create a "series axis range" and make it draggable, dynamically adjusting threshold lines and respective series fills.
See the Pen amCharts 4: Draggable series axis ranges by amCharts team (@amcharts) on CodePen.24419