Offset/Match? Chart by selected start/end date and col header

here's a macro sol'n:

Option Explicit

Private Sub UpdateChart_Click()
    Dim AbsissaRange    As String, _
        OrdinateRange   As String, _
        OrdinateColumn  As Long, _
        StartMonthRow   As Long, _
        EndMonthRow     As Long, _
        DateSearchRange As String
        
    DateSearchRange = Range("a1").CurrentRegion.Resize(, 1).Address(0, 0)
    
    StartMonthRow = WorksheetFunction.Match(Range("K8"), Range(DateSearchRange), 0)
    EndMonthRow = WorksheetFunction.Match(Range("K10"), Range(DateSearchRange), 0)
    AbsissaRange = Range(Cells(StartMonthRow, 1), Cells(EndMonthRow, 1)).Address(0, 0)
    
    OrdinateColumn = WorksheetFunction.Match(Range("N1"), Range("A1:H1"), 0)
    OrdinateRange = Range(Cells(StartMonthRow, OrdinateColumn), Cells(EndMonthRow, OrdinateColumn)).Address(0, 0)
    
    
    ChartObjects("Chart 3").Activate
    ActiveChart.SeriesCollection(1).XValues = _
        "='Index-Match w-Variable Date'!" & AbsissaRange
        
    ActiveChart.SeriesCollection(1).Name = "='Index-Match w-Variable Date'!" & Cells(1, OrdinateColumn).Address(0, 0)
    ActiveChart.SeriesCollection(1).Values = _
        "='Index-Match w-Variable Date'!" & OrdinateRange
    Range("A1").Select

End Sub