Answer
To create birthday reminders for your active employees, go to Settings >> Reminders. Tick the Birthday Reminders On? box at the bottom-left of the screen, choose how many days' notice you want, then click Create Birthday Reminders For Active Employees. This adds a birthday reminder for every active employee.
You can edit an individual reminder by clicking the pencil icon and saving your changes, or remove a single employee's reminder by clicking the red X on their row. To clear all birthday reminders at once, untick Birthday Reminders On? at the bottom-left of the screen.
When you open Lightning Payroll on or around the date each reminder is set for, you are notified with a pop-up.
