要更改amCharts堆叠柱状图中工具提示的位置，您可以使用tooltip的textAlign属性来指定对齐方式。以下是一个包含代码示例的解决方法：

// 创建堆叠柱状图
var chart = am4core.create("chartdiv", am4charts.XYChart);

// 设置数据
chart.data = [{
  "category": "类别1",
  "value1": 10,
  "value2": 15,
  "value3": 20
}, {
  "category": "类别2",
  "value1": 5,
  "value2": 8,
  "value3": 12
}];

// 创建类别轴
var categoryAxis = chart.xAxes.push(new am4charts.CategoryAxis());
categoryAxis.dataFields.category = "category";

// 创建值轴
var valueAxis = chart.yAxes.push(new am4charts.ValueAxis());

// 创建柱状图系列
var series1 = chart.series.push(new am4charts.ColumnSeries());
series1.dataFields.valueY = "value1";
series1.dataFields.categoryX = "category";
series1.name = "系列1";

var series2 = chart.series.push(new am4charts.ColumnSeries());
series2.dataFields.valueY = "value2";
series2.dataFields.categoryX = "category";
series2.name = "系列2";

var series3 = chart.series.push(new am4charts.ColumnSeries());
series3.dataFields.valueY = "value3";
series3.dataFields.categoryX = "category";
series3.name = "系列3";

// 创建图例
chart.legend = new am4charts.Legend();

// 更改工具提示位置
series1.tooltip.pointerOrientation = "vertical";
series1.tooltip.getFillFromObject = false;
series1.tooltip.background.fill = am4core.color("#000");
series1.tooltip.background.pointerLength = 0;
series1.tooltip.dx = 20; // 定义水平偏移量
series1.tooltip.dy = -10; // 定义垂直偏移量
series1.tooltip.label.textAlign = "left"; // 定义文本对齐方式

series2.tooltip.pointerOrientation = "vertical";
series2.tooltip.getFillFromObject = false;
series2.tooltip.background.fill = am4core.color("#000");
series2.tooltip.background.pointerLength = 0;
series2.tooltip.dx = 20;
series2.tooltip.dy = -10;
series2.tooltip.label.textAlign = "left";

series3.tooltip.pointerOrientation = "vertical";
series3.tooltip.getFillFromObject = false;
series3.tooltip.background.fill = am4core.color("#000");
series3.tooltip.background.pointerLength = 0;
series3.tooltip.dx = 20;
series3.tooltip.dy = -10;
series3.tooltip.label.textAlign = "left";

在上面的代码中，我们使用dx和dy属性来指定工具提示的水平和垂直偏移量。您可以根据需要调整这些值来更改工具提示的位置。此外，我们还使用textAlign属性来将文本对齐方式设置为左对齐。

请注意，上述代码假设您已经正确引入了amCharts库，并在页面上有一个id为chartdiv的元素用于显示图表。