This code will do it, but we need to find a way for your db to run it.
1. via the AutoExec macro (a bit complicated).
2. In the Form_Open event, if your db automatically opens a form when it starts (easiest).
Code:
Public Sub CheckSeason()
Dim sSQL As String
Dim strSeas As String
strSeas = Year(Date) & "-" & Year(Date) + 1
'Debug.Print strSeas
If Month(Date) <> 9 Then Exit Sub
If DLookup("Season", "Jaren", "Season='" & strSeas & "'") = strSeas Then Exit Sub
sSQL = "INSERT INTO Jaren (Season) VALUES ('" & strSeas & "')"
CurrentDb.Execute sSQL, dbFailOnError
End Sub