Prerequisites
You must be:
an admin of the Confluence Cloud site
either a technical contact or billing contact of the Confluence Cloud instance
To verify, log in to MyAtlassian and ensure the Confluence Cloud instance appears on the Licenses page.
Guide
In your Confluence Cloud site
choose the Confluence icon in the top-left corner
go to Apps > Find new apps
When the Find new apps screen loads, search for Page Approval for Confluence
choose Install (or Free Trial if the app requires a paid license) to download and install
If the app requires a paid license, you will be provided with a minimum of a 30-day free trial.
Once Atlassian confirm that the app has been installed - you're all set!
choose Close in the Installed and ready to go dialog window