What is the quality management process in QGM, and what should you do if building change management from scratch?

It's the governance body QGM follows — systematically controlling changes across the landscape. SAP provides the framework/structure/best-practice process out of the box; your org must understand it, judge fit, and handle gaps (change your process or the tool settings).

If building a change-management system from scratch, use SAP's standard process as the baseline.