public int FieldOrder {get; set;}

//Note: Call within QueuedTask.Run()
//The fields in the datasource used for the report
//This uses a US Cities dataset
var listFields = new List<CIMReportField> {
          //Grouping should be the first field
          new CIMReportField{Name = "STATE_NAME", FieldOrder = 0, Group = true, SortInfo = FieldSortInfo.Desc}, //Group cities using STATES
          new CIMReportField{Name = "CITY_NAME", FieldOrder = 1},
          new CIMReportField{Name = "POP1990", FieldOrder = 2, },
      };
//Definition query to use for the data source
var defQuery = "STATE_NAME LIKE 'C%'";
//Define the Datasource
var reportDataSource = new ReportDataSource(featureLayer, defQuery, listFields);
//The CIMPage defintion - page size, units, etc
var cimReportPage = new CIMPage
{
  Height = 11,
  StretchElements = false,
  Width = 6.5,
  ShowRulers = true,
  ShowGuides = true,
  Margin = new CIMMargin { Bottom = 1, Left = 1, Right = 1, Top = 1 },
  Units = LinearUnit.Inches
};

//Report template
var reportTemplates = await ReportTemplateManager.GetTemplatesAsync();
var reportTemplate = reportTemplates.Where(r => r.Name == "Attribute List with Grouping").First();

//Report Styling
var reportStyles = await ReportStylingManager.GetStylingsAsync();
var reportStyle = reportStyles.Where(s => s == "Cool Tones").First();

//Field Statistics
var fieldStatisticsList = new List<ReportFieldStatistic> {
          new ReportFieldStatistic{ Field = "POP1990", Statistic = FieldStatisticsFlag.Sum}
          //Note: NoStatistics option for FieldStatisticsFlag is not supported.
      };
var report = ReportFactory.Instance.CreateReport("USAReport", reportDataSource, cimReportPage, fieldStatisticsList, reportTemplate, reportStyle);

//This is the gap between two fields
double fieldIncrement = 0.9388875113593206276389;
//On the QueuedTask
//New field to add.
var newReportField = new CIMReportField
{
  Name = "POP1990",
  FieldOrder = 2,
};
//Get the "ReportSection element"                
var mainReportSection = report.Elements.OfType<ReportSection>().FirstOrDefault();
if (mainReportSection == null) return;

//Get the "ReportDetails" within the ReportSectionElement. ReportDetails is where "fields" are.
var reportDetailsSection = mainReportSection?.Elements.OfType<ReportDetails>().FirstOrDefault();
if (reportDetailsSection == null) return;

//Within ReportDetails find the envelope that encloses a field.
//We get the first CIMParagraphTextGraphic in the collection so that we can add the new field next to it.                    
var lastFieldGraphic = reportDetailsSection.Elements.FirstOrDefault((r) =>
{
  var gr = r as GraphicElement;
  if (gr == null) return false;
  return (gr.GetGraphic() is CIMParagraphTextGraphic ? true : false);
});
//Get the Envelope of the last field
var graphicBounds = lastFieldGraphic.GetBounds();

//Min and Max values of the envelope
var xMinOfFieldEnvelope = graphicBounds.XMin;
var yMinOfFieldEnvelope = graphicBounds.YMin;

var xMaxOfFieldEnvelope = graphicBounds.XMax;
var YMaxOfFieldEnvelope = graphicBounds.YMax;
//create the new Envelope to be offset from the existing field
//At 2.x
//MapPoint newMinPoint = MapPointBuilder.CreateMapPoint(xMinOfFieldEnvelope + fieldIncrement, yMinOfFieldEnvelope);
//MapPoint newMaxPoint = MapPointBuilder.CreateMapPoint(xMaxOfFieldEnvelope + fieldIncrement, YMaxOfFieldEnvelope);
//Envelope newFieldEnvelope = EnvelopeBuilder.CreateEnvelope(newMinPoint, newMaxPoint);

MapPoint newMinPoint = MapPointBuilderEx.CreateMapPoint(xMinOfFieldEnvelope + fieldIncrement, yMinOfFieldEnvelope);
MapPoint newMaxPoint = MapPointBuilderEx.CreateMapPoint(xMaxOfFieldEnvelope + fieldIncrement, YMaxOfFieldEnvelope);
Envelope newFieldEnvelope = EnvelopeBuilderEx.CreateEnvelope(newMinPoint, newMaxPoint);

//Create field
GraphicElement fieldGraphic = ReportElementFactory.Instance.CreateFieldValueTextElement(reportDetailsSection, newFieldEnvelope, newReportField);