Make sure you're in 'Plan' mode.
Click on the 'Stops' tab at the top of your screen.
To add a new stop, click on the '+' sign.
When you return to the dashboard, the stop will appear in the unscheduled bar.
Click 'Insert unscheduled' so Routific can insert these new stops into your existing routes.
Note: Once you've dispatched, you can insert unscheduled stops or make manual changes to routes. But reoptimizing your entire solution is not possible after you have dispatched routes to the drivers.