From the Autopilot screen, tap on a piece of feedback that was merged. It displays the feedback it was merged into, with an "Unmerge" button.

Tapping the "Unmerge" button here looks like it succeeds, but it actually fails. Silently.

Only when I went into the actual feedback itself (not the "peek" window from autopilot) and clicked the "Unmerge" button did it work properly.