How to mass clear notifications from bell when Synchronize Bell Notifications only does 500 at a tim

We have notifications/approvals being approved through email and we need to have the bell cleared so that possible double approval does not occur.  We run the Synchronize Bell Notifications but the query provided from Oracle states we have over 21000 notifications.  How can we clear these as we know of many cases where the email was approved but not being updated by Synchronize Bell Notifications?