вы можете использовать это
Option Explicit
Sub main()
Dim cell As Range, nCols As Long
With ActiveSheet.UsedRange.SpecialCells(xlCellTypeBlanks)
For Each cell In .Cells
nCols = WorksheetFunction.Min(cell.Column - 1, 3)
If Intersect(cell.Offset(, -nCols).Resize(, nCols + 1), .Cells).Count < 4 Then cell.Value = "x"
Next
End With
End Sub