Atlassian’s document describes how to install apps, including Excel-like Tables for Confluence:
Manage your apps (Confluence Cloud)
See Find and add new apps section for the details.
You can also add it You can install our app from Atlassian Marketplace. Go to marketplace.atlassian.com and search Excel-like Tables for Confluence. You will find ‘Try it freefree’ button at the upper-right corner.
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