early 2009 imac reinstall snowleopard
i tried to reset my early 2009 iMac to factory settings so we restarted it and erased using disk utility. When we tried to reinstall OS X it suggests El Capitan so we put in my Apple ID (not the original one for the iMac as we got it second hand) but it says the item is temporarily available. How can I reinstall OS X to my iMac?
iMac, OS X 10.11