Quick installation 

In a composer-based TYPO3 installation you can install the extension rd_comments via composer:

composer require remotedevs/rd-comments
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In TYPO3 installations above version 11.5, the extension will be automatically installed. You do not have to activate it manually.

Update the database schema 

Open your TYPO3 backend with system-maintainer permissions.

In the module menu to the left, navigate to Admin Tools > Maintenance, then click on Analyze database and apply all suggested changes.

TYPO3 Analyze Database screen

Clear all caches 

In the same module Admin Tools > Maintenance, you can also conveniently clear all caches by clicking the button Flush cache.

TYPO3 Flush Cache screen