Rule to Notify Preparer on Reopened Reconciliation

Hi Team,

Earlier, my reconciliation was submitted because the source and sub-system balances matched, and the unexplained difference was zero rule executed. Later, the source balance changed, so the reconciliation reopened and went back to the Preparer. Now, I want to create a rule that triggers an alert to the Preparer when a reconciliation is reopened? How can i create this rule?