User Form field inserts wrong date format

If the date is in format dd/mm/yyyy you can try to use this code (here I suppose your data field in form is called 'Textbox1'):

Private Sub Macro1()
   Dim myDate As Date
   myDate = DateSerial(Mid(TextBox1.Text, 7, 4), _
                       Mid(TextBox1.Text, 4, 2), _
                       Mid(TextBox1.Text, 1, 2))
   Range("A1") = myDate
End Sub

Regards,
Antonio