That was for the multiple undos, which it said it could do (and what you wanted).

But it's also easy to know which textbox was last edited.

Code:
Dim lastedit As Integer

Private Sub Form_Load()
lastedit = 0
End Sub

Private Sub Text1_Change()
lastedit = 1
End Sub

Private Sub Text2_Change()
lastedit = 2
End Sub

Private Sub Text3_Change()
lastedit = 3
End Sub

Private Sub Command1_Click()
If lastedit = 0 Then
Exit Sub 'no textbox edited
ElseIf lastedit = 1 Then
Text1.SetFocus
SendKeys "^z", True
'text1 last edited
ElseIf lastedit = 2 Then
Text2.SetFocus
SendKeys "^z", True
'text2 last edited
ElseIf lastedit = 3 Then
Text3.SetFocus
SendKeys "^z", True
'text3 last edited
End If
End Sub