Update values when linked data validation list changes

Use Change event in VBA to achieve this 

example below data validation list source in F7:F10, B3:B4 are two dropdowns

Private Sub Worksheet_Change(ByVal Target As Range)
Application.ScreenUpdating = False
Dim count_cells As Integer
Dim new_value As String
Dim old_value As String
For count_cells = 1 To Range("F6").CurrentRegion.Rows.Count - 1
    If Intersect(Target, Range("F" & count_cells + 6)) Is Nothing Then
    Else
        Application.EnableEvents = False
        new_value = Target.Value
        Application.Undo
        old_value = Target.Value
        Target.Value = new_value
        Range("B3:B4").Select
        Selection.Replace What:=old_value, Replacement:=new_value, LookAt:=xlPart, _
        SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
        ReplaceFormat:=False
        Target.Select
    End If
Next count_cells
Application.EnableEvents = True
Application.ScreenUpdating = True
End Sub