Navigate to the Calendar Sync page in Reclaim
Click the + New Sync button at the bottom of the page.
Under the Sync from section, click the downward arrow next to the box showing only your email address to see a list of your shared calendars associated with your Google account.
Select the shared calendar you want to sync.
Click Next: Preferences.
Customize your syncing details.
Click Start Syncing.
Learn more on the differences between Primary and shared calendar.