Your error message told you what the problem is. Your description simply said you have a three column table. Your picture is not a three column table. It is a complex table with vertically merged rows. Do people pay you to sell cars? You should hire someone and pay them to write your code.
Private Sub Document_ContentControlOnExit(ByVal ContentControl As ContentControl, Cancel As Boolean)
Dim lngIndex As Long
Select Case ContentControl.Title
Case "Model"
For lngIndex = 1 To ContentControl.DropdownListEntries.Count
If ContentControl.Range.Text = ContentControl.DropdownListEntries(lngIndex).Text Then
ContentControl.Range.Cells(1).Next.Next.Next.Next.Next.Next.Range.Text = ContentControl.DropdownListEntries.Item(lngIndex).Value
'ContentControl.Range.Rows(1).Cells(3).Range.Text = ContentControl.DropdownListEntries.Item(lngIndex).Value
Exit For
End If
Next lngIndex
End Select
lbl_exit:
Exit Sub
End Sub