Code

Sub UnmergeAndFillInTheBlanks()

    Dim cell As Range, LR As Long, rng As Range
    
    Const Colnum As String = "A:N"
        
    Application.ScreenUpdating = False
    Columns(Colnum).UnMerge
    LR = Cells.Find("*", , , , xlByRows, xlPrevious).Row
    Set rng = Intersect(Rows(2 & ":" & LR), Columns(Colnum))
    On Error Resume Next
    For Each cell In rng.SpecialCells(xlCellTypeBlanks).Cells
        cell.Value = cell.Rows(1).Offset(-1).Value
    Next
    Application.ScreenUpdating = True
End Sub