Event alerts can be created (for custom events) and configured (for alert events, and custom events with a previously created alert) from the Event Details panel:
From the Events module, select the event from the feed to open the Event Details panel.
Open the Configure Alert panel:
For existing alerts, click Edit Alert.
For new alerts, click Create Alert from Event.
Configure the alert as necessary.
New alerts will be auto-filled with information from the custom event.
For more information on configuring alerts, see Alerts.
Click Create for new alerts. For existing alerts, click Save to apply the changes.