You can make a copy of an existing feed by duplicating it from the My Feeds page at https://app.helloaudio.fm/my-feeds
Click the dropdown at the right of the feed, and select Duplicate.
You can also find this inside the feed under Feed Details, then click Duplicate Feed.
Choose the new feed type, then Confirm.
You can duplicate a private feed into a public feed, but that requires setting various properties of the public feed that aren't in the private feed. You'll be prompted to set them when duplicating.
A duplicated feed includes all the episodes and settings, but will not have any listeners or downloads. It is an archived feed when created. You can activate it when you're ready by viewing in your list of feeds at https://app.helloaudio.fm/my-feeds.