First, set configuration for notification template. Go to Notifications → Configuration → green button Add
Notification is implemented as long running task. You must go to Settings → Task scheduler → Scheduled tasks and in the agenda just plan new long running task with name Notification of expiring and expired guarantors (ExtrasExpiredGuaranteeNotificationTaskExecutor).
Please note that for every run of the task, it evaluates the conditions and sends notifications again for all roles that meet the criteria, even if they were already notified previously. This is intentional behavior.
The long running task has these configurations: