The following code sends a chart to a new instance of Powerpoint. How can it be modified to send to an existing presentation? 
Sub ExportChartsToPowerPoint()
    Dim pptApp As Object
    Dim pptPres As Object
    Dim chartObj As ChartObject
    Dim slideIndex As Integer
    ' Create a new instance of PowerPoint application
    Set pptApp = CreateObject("PowerPoint.Application")
    pptApp.Visible = True ' Make PowerPoint visible
    ' Create a new presentation
    Set pptPres = pptApp.Presentations.Add
    slideIndex = 1 ' Initialize slide index
    ' Loop through each chart object in the worksheet
    For Each chartObj In Sheets("Slide 11").ChartObjects
        With chartObj.Chart
            ' Copy the chart
            .ChartArea.Copy
            ' Paste the chart into PowerPoint
            pptPres.Slides.Add slideIndex, 1 ' Add a new slide
            pptPres.Slides(slideIndex).Shapes.PasteSpecial
            ' Adjust the position and size of the pasted chart
            With pptPres.Slides(slideIndex).Shapes(1)
                .Left = 100 ' Adjust the left position as needed
                .Top = 100 ' Adjust the top position as needed
                .Width = 400 ' Adjust the width as needed
                .Height = 300 ' Adjust the height as needed
            End With
            slideIndex = slideIndex + 1 ' Increment slide index
        End With
    Next chartObj
    ' Clean up
    Set pptPres = Nothing
    Set pptApp = Nothing 
End Sub


Actually, on second thoughts, how could it be modified to send a selected chart to a selected powerpoint presentation?