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

{
  //Note: 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();
}

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

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

  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

  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);
}