Welcome to Android Central. Please register an account to reply to this thread. This link will help you do that...
https://forums.androidcentral.com/as...-new-post.html
Access to the Ringtone folder seems to have gone the way of the Dodo. Anymore to add items you'll likely need an app for that. Zedge is probably one of the more well known apps but there are hundreds on the Play Store.
Not sponsored by anyone, but Zedge will allow you to create content from your own library as well as search from an extensive online archive. It will also let you manage the items you've downloaded, move, delete, save to specific locations. The latter being where you would be able to put something in with the notifications.