1. In property browser set Alignable property of UserControl to True.
2. In Resize event of UserControl put this code:

Option Explicit

Private Sub UserControl_Resize()
  
  Extender.Align = vbAlignTop
End Sub

You can change vbAlignTop constant to vbAlignBottom, vbAlignLeft or vbAlignRight if you want control to aligns bottom, left or right respectively.