Perusall provides an assignment calendar that you can subscribe to from the calendar on your computer or phone; depending on your calendar app's settings and capabilities, the calendar can also update automatically if new assignments are added or if due dates change.
To subscribe to your personal assignment calendar, click Add to my calendar on the left panel of your course home page in Perusall. From there you'll get a special address that you can paste into your calendar app.
To subscribe to the calendar in your calendar app: