Open the project you wish to sync, then click Calendar in the left sidebar.

Once you are viewing the calendar, select the three-dot button from the upper right-hand corner and then click Sync Calendar from the dropdown.

A pop-up with three tabs appears. Select the Microsoft Outlook tab.

Next, follow these steps:
Copy the generated URL, then navigate to your Outlook Calendar.
Click Add Calendar and select the Subscribe from the Web option.
Paste the URL here, and click Import.
NOTE: While your Assemble calendar should sync immediately, future updates in Assemble may take up to a day to appear in your external calendar based on your Microsoft Outlook settings.