public class ReportDetails : ReportSectionElement, ArcGIS.Desktop.Mapping.IElement, ArcGIS.Desktop.Mapping.IElementContainer, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IDisposable, System.IEquatable<Element>  

//On the QueuedTask
var detailsSection = report.Elements.OfType<ReportSection>().FirstOrDefault().Elements.OfType<ReportDetails>().FirstOrDefault();
var bounds = detailsSection.GetBounds();
ReportView.Active.ZoomTo(bounds);

//Get the "ReportSection element"
//ReportSectionElement contains the ReportHeader, ReportPageHeader, ReportDetails. ReportPageFooter, ReportFooter sections.
var mainReportSection = report.Elements.OfType<ReportSection>().FirstOrDefault();

//Get the ReportHeader
var reportHeader = mainReportSection?.Elements.OfType<ReportHeader>().FirstOrDefault();

//Get the ReportHeader
var reportPageHeader = mainReportSection?.Elements.OfType<ReportPageHeader>().FirstOrDefault();

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

//Get the ReportPageFooter
var reportPageFooter = mainReportSection?.Elements.OfType<ReportPageFooter>().FirstOrDefault();

//Get the ReportFooter
var reportFooter = mainReportSection?.Elements.OfType<ReportFooter>().FirstOrDefault();

//ReportDetailsSection contains the "Fields"

var elements = reportDetailsSection.Elements;
reportDetailsSection.SelectElements(elements);

//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);