Try this
Option Explicit
Sub UnmergeAndFill()
Dim rowLast As Long, i As Long
Dim aryAreas() As Range
Dim cntAreas As Long
With Worksheets("HIN")
rowLast = .Cells(.Rows.Count, 4).End(xlUp).Row
i = 2
Do While i <= rowLast
If .Cells(i, 4).MergeCells Then
cntAreas = cntAreas + 1
ReDim Preserve aryAreas(1 To cntAreas)
Set aryAreas(cntAreas) = .Cells(i, 4).MergeArea
End If
i = .Cells(i, 4).End(xlDown).Row
Loop
For i = LBound(aryAreas) To UBound(aryAreas)
aryAreas(i).UnMerge
aryAreas(i).Value = aryAreas(i).Cells(1, 1).Value
Next i
End With
MsgBox "Done"
End Sub