Попробуйте следующий код, пожалуйста:
Sub SumSales()
Dim sh As Worksheet, rngS As Range, lastRow As Long
For Each sh In ActiveWorkbook.Sheets 'iterate through all sheets
'find the cell having "Sales" text/value
Set rngS = sh.Range(sh.Cells(1, 1), sh.Cells(1, _
sh.Cells(1, Columns.count).End(xlToLeft).Column)).Find("Sales")
'if the cell has been found (the cell range is NOT Nothing...)
If Not rngS Is Nothing Then
'Determine the last row of the found cell column:
lastRow = sh.Cells(Rows.count, rngS.Column).End(xlUp).row
'Write the Sum formula in the last empty cell:
rngS.Offset(lastRow).formula = "=Sum(" & rngS.Offset(1).address & _
":" & sh.Cells(lastRow, rngS.Column).address & ")"
sh.Range("A" & lastRow + 1).Value = "Sum of sales is:"
Else
'if any cell has been found, it returns in Immediate Window (Being in VBE, Ctrl + G) the sheet names not having "Sales" header:
Debug.Print "No ""Sales"" column in sheet """ & sh.name & """."
End If
Next
End Sub