Call ZoomBy method of SciChart control from ViewModel Class

I am trying to call the ZoomBy() method of SciChart control from ViewModel. The ZoomBy() is easily available in the xaml.cs file like below:

// TODO: Need to implement zoom using MVVM
    private void BtnZoomIn_Click(object sender, RoutedEventArgs e)
    {
        TemperatureGraph.ChartModifier.XAxis.ZoomBy(-0.1, -0.1);
    }

The same functionality I need to implement using the ViewModel pattern.

However the ZoomExtents method is easily being called using ViewportManager of SciChart control. E.g. below: XAML file

<RocheButton Name="BtnZoomOut" DockPanel.Dock="Top" Icon="{IconResource Icon=ZoomOut}" HorizontalAlignment="Right" Command="{Binding ZoomOutCommand}" />    
<s:SciChartSurface x:Name="TemperatureGraph" Grid.Column="0" s:ThemeManager.Theme="BrightSpark"  
                           RenderableSeries="{s:SeriesBinding TemperatureGraphViewModel}" DockPanel.Dock="Bottom"
                           ViewportManager="{Binding ViewportManager}">

And the ViewModel Code:

public class TemperatureSummaryGraphViewModel : ViewModelBase
    {
        #region Private Members

        private IXyDataSeries<TimeSpan, double> TemperatureDataSeries = new XyDataSeries<TimeSpan, double>();
        private IXyDataSeries<TimeSpan, double> AcquisitionPointDataSeries = new XyDataSeries<TimeSpan, double>();
        private DefaultViewportManager _viewportManager = new DefaultViewportManager();
        private ICommand _zoomOutCommand;

        #endregion

        #region Constructor

        public TemperatureSummaryGraphViewModel()
        {
            ZoomOutCommand = new DelegateCommand(() => ZoomOutTemperatureGrpah());
            GenerateDummySeries();

            TemperatureGraphViewModel.Add(new LineRenderableSeriesViewModel()
            {
                DataSeries = TemperatureDataSeries,
                StyleKey = "LineSeriesStyle0"
            });

            TemperatureGraphViewModel.Add(new XyScatterRenderableSeriesViewModel()
            {
                DataSeries = AcquisitionPointDataSeries,
                StyleKey = "ScatterSeriesStyle0"
            });
        }

        #endregion

        #region Public Properties

        public ObservableCollection<IRenderableSeriesViewModel> TemperatureGraphViewModel { get; } = new ObservableCollection<IRenderableSeriesViewModel>();

        public IViewportManager ViewportManager
        {
            get
            {
                return _viewportManager;
            }

            set
            {
                if (ReferenceEquals(value, _viewportManager))
                {
                    return;
                }

                _viewportManager = (DefaultViewportManager)value;
                OnPropertyChanged("ViewportManager");
            }
        }

        public ICommand ZoomOutCommand
        {
            get
            {
                return _zoomOutCommand;
            }

            set
            {
                if (ReferenceEquals(value, _zoomOutCommand))
                {
                    return;
                }

                _zoomOutCommand = value;
                OnPropertyChanged(nameof(ZoomOutCommand));
            }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// To generate dummy data
        /// // TODO: Need to integrate it with RunEditor with the actual data
        /// </summary>
        public void GenerateDummySeries()
        {
            double y = 80.5, yVar = 30.0;

            TemperatureDataSeries.Append(TimeSpan.FromMinutes(1), 40.0);
            TemperatureDataSeries.Append(TimeSpan.FromMinutes(2), 80.5);
            for (int x = 2; x < 50; x++)
            {
                TemperatureDataSeries.Append(TimeSpan.FromMinutes(x), y);

                yVar *= -1;
                y += yVar;
            }

            for (var i = 5.4; i < 50; i += 2)
            {
                AcquisitionPointDataSeries.Append(TimeSpan.FromMinutes(i), 60.0);
            }
        }

        public void ZoomOutTemperatureGrpah()
        {
            _viewportManager.ZoomExtents();
        }

        #endregion
    }
}

This code is working fine and zooming out the scichart control to 100%.

I want to implement the same using the ZoomBy().

Please help!