You can copy episodes from one feed to another using the bulk editing feature of episodes.
Check the box next to each episode you'd like to copy, or select all
Click on the "Copy to Another Feed" icon
Choose your feed
Click "Confirm"
All episodes are copied as "unpublished" in the destination feed. The position in the feed depends on the type of feed you're copying to.
Instant: At the bottom of the feed.
Date-based: Set to the date and time at the time of copying.
Drip: At the bottom of the feed.
After copying, head to your destination feed and finalize any settings like scheduled release or position, and publish the copied episodes when ready