Transform data in Appian

What chart are you using? You can directly use grouping on the chart level. 

"Column Chart"

And do you also have a record for this table with the sync enabled?

If yes, you can pass that record type directly in the chart and set the primary grouping on your 'date_month' field

If not, then you can achieve it by this block of code. 

a!localVariables(
  local!data: {
    {
      date_month: 1,
      templateId_count: 3,
      templateName: "Accident / Near Miss"
    },
    {
      date_month: 1,
      templateId_count: 22,
      templateName: "DFTCLousado"
    },
    {
      date_month: 1,
      templateId_count: 12,
      templateName: "Duplicated items process"
    },
    {
      date_month: 1,
      templateId_count: 3,
      templateName: "ESP Summary Report"
    },
    {
      date_month: 1,
      templateId_count: 2,
      templateName: "Every Month"
    }
  },
  local!uniqueDateMonths: union(
    local!data.date_month,
    local!data.date_month
  ),
  {
    a!columnChartField(
      label: "Column Chart",
      categories: local!data.templateName,
      series: a!forEach(
        items: local!uniqueDateMonths,
        expression: a!chartSeries(
          label: fv!item,
          data: index(
            local!data.templateId_count,
            wherecontains(
              fv!item,
              tointeger(local!data.date_month)
            ),
            {}
          )
        )
      ),
      stacking: "NONE",
      showLegend: true,
      showTooltips: true,
      labelPosition: "ABOVE",
      allowImageDownload: true,
      colorScheme: "RAINFOREST",
      height: "MEDIUM",
      xAxisStyle: "STANDARD",
      yAxisStyle: "STANDARD"
    )
  }
)