I don’t think I’m following exactly what you have done here. Are you trying to use an older copy of the El Capitan installer that you stored away or did you follow the steps outlined in https://support.apple.com/HT206886 and downloaded the corrected version as directed in Step 4?
When it starts up in the El Capitan installer, can you not just quit the installer?
The date to use an older copy is Oct 23 or earlier, but not sure how you will be able reset it.