Click on Message with sound and choose an alarm chime. In the pop-up menu click Custom…, then Message.Enter the time that you want the alarm to go off, then click on None next to alert.Enter the name for your event, then click on the date and time section.Right-click your preferred time slot and select New Event.Double-click the date that you want to set the alarm on.Click on the Launchpad, then click on the Calendar app.To set a one-time alarm, you have to first create an event. The Apple Calendar is the place for all things schedule-related, including alarms. Try free ✕ How to set an alarm on Mac with the Apple Calendar