This tutorial assumes that you have completed the creation of an iCal feed and you have the feed URL at hand. For more details see Creating an iCal feed.
1. In the Office 365 Calendar app click on the "Add calendar" menu and select the "From internet" option.
2. In the newly appeared sidebar panel paste the URL of your YArooms iCal feed in the "Link to the calendar" field, give it a name of your choosing and click the "Save" button.
3. The new calendar will appear in the list of "Other calendars" on the left and its events shown on the main calendar. Office 365 updates the calendar periodically by checking the iCal feed for changes. If you delete the iCal feed from the Integrations section, then Microsoft Office will not be able to update the calendar anymore.