To access the Space configuration of Slack for Confluence, click on the Spaces dropdown next to the Confluence logo in the upper-left-hand corner and select View all spaces.
Here, click on the Action menu ··· to access the Space settings page of the space you want to set up notifications for.
Now navigate to App links in the left navigation bar. Underneath, select the Slack for Confluence tab.
Here, you can again set up Slack channels and users to be notified of any updates that are checked under the When to show notifications section.