From a conversation you can undo at most 200 changes, at most 7 days back. The assistant previews the rollback and you confirm. An undo the assistant prepared expires after 10 minutes; ask it to prepare the undo again.
Undo restores a field only if the value is still the one Heldrey wrote. Otherwise it reports a conflict. Conflicts become Needs attention items rather than silent overwrites. That is the promise that makes undo safe to offer.
See Activity and undo.