Activation de checkbox

Private Sub CommandButton1_Click()
  Userform1.checkboxa = (lblNiv3 = 1)
  Userform1.CheckBoxb = (lblNiv3 = 2)
  Userform1.CheckBoxc = (lblNiv3 = 3)
  Unload Userformx
  Userform1.Show
End Sub

Private Sub CommandButton1_Click() 'bouton"ok"
Unload userformx
Select Case Me.lblNiv3.Caption 'agit en fonction de la liste déroulante
Case "1"
userform1.checkboxa.value=true
userform1.Show ' ici l'userform1 s'ouvre mais comment faire pour que checkbox a soit activé?
Case "2"
userform1.checkboxb.value=true
userform1.Show ' idem pour le checkbox b
Case "3"
userform1.checkboxc.value=true
userform1.Show ' idem pour le checkbox c
End Select
End Sub

if userformx.listebox.value=1 hten
userform1.checkboxa.value=true
elseif userformx.listebox.value=2 hten
userform1.checkboxb.value=true
elseif userformx.listebox.value=3 hten
userform1.checkboxc.value=true
end if
userform1.show