To set reminders relating to a schedule item, first navigate to the relevant Job > Project Management > Schedule and double-click the relevant schedule item.

A pop-up will appear (shown below). On the left of the pop-up, below the attachments button, you can select the Reminder icon (bell). You can add different contacts to be reminded of the upcoming scheduled item. You can also set how many days before the scheduled item starts or ends for the reminder to be sent.