Tap + on the episode, then choose Play next or Add to queue.
- Play next puts it right after the episode that's playing.
- Add to queue puts it at the end of Up Next.
Once it's added, the + turns into a purple −. To take it out again, tap − and choose Remove from queue.
To add a whole list at once (your Timeline, Saved, Downloads or a playlist), use Add all at the top of the list.