Need help to find the Sum of all the Cell in below

I think that this will do what you want

Sub test()
    Dim oneArea As Range
    Dim LastPair As Range, PairFtn As String
    
    For Each oneArea In Range("AG:AG").SpecialCells(xlCellTypeConstants, xlNumbers).Areas
        With oneArea.Cells(1, 1).Offset(-1, 0)
            If .Offset(-1, 0).Value = vbNullString Then
                If Not LastPair Is Nothing Then
                    LastPair.FormulaR1C1 = PairFtn
                End If
                Set LastPair = .Offset(-1, 0)
                PairFtn = "=" & .Address(True, True, xlR1C1)
            Else
                PairFtn = PairFtn & "+" & .Address(True, True, xlR1C1)
            End If
            .FormulaR1C1 = "=SUM(" & oneArea.Address(True, True, xlR1C1) & ")"
        End With
    Next oneArea
    If Not LastPair Is Nothing Then
        LastPair.FormulaR1C1 = PairFtn
    End If
End Sub