Sub BulkUpdateTutor()
Dim i As Long, j As Long, OldTutor As String, NewTutor As String
OldTutor = Trim(InputBox("Old Tutor"))
NewTutor = Trim(InputBox("New Tutor", , OldTutor))
If OldTutor = "" Then Exit Sub
With ActiveDocument
  For i = 1 To .SelectContentControlsByTitle("Subject").Count
    With .SelectContentControlsByTag("Subject_" & i)(1)
      For j = 1 To .DropdownListEntries.Count
        With .DropdownListEntries(j)
          If Trim(.Value) = OldTutor Then
            .Value = Replace(.Value, OldTutor, NewTutor)
          End If
        End With
      Next
    End With
  Next
End With
End Sub