Is this what you are trying?
Also if you are trying to save it as jpg then why a png filter? I have changed “myChart.jpg” to “myChart.png”. Change as applicable.
Sub ExportChart()
Dim objChrt As ChartObject
Dim myChart As Chart
Set objChrt = Sheets("Graphs").ChartObjects(3)
Set myChart = objChrt.Chart
myFileName = "myChart.png"
On Error Resume Next
Kill ThisWorkbook.Path & "\" & myFileName
On Error GoTo 0
myChart.Export Filename:=ThisWorkbook.Path & "\" & myFileName, Filtername:="PNG"
MsgBox "OK"
End Sub