code: public void goToStep(MaterialStep step) {
          for (int i = 0; i < getWidgetCount(); i++) {
              Widget w = getWidget(i);
              if (w instanceof MaterialStep) {
                  MaterialStep materialStep = (MaterialStep) w;
                  boolean active = materialStep.equals(step);
                  materialStep.setActive(active);
                  if (active) {
                      setCurrentStepIndex(i);
                  }
              }
          }
      }
docs: Go to the specfic {@link MaterialStep}.