In the command line for Magento 2, you need to install the Migration Tool.
To Find out your version of Magento 2
php <magento_root>/bin/magento --version
To install Migration Tool (change version number on the end to match yours)
composer require magento/data-migration-tool:2.4.1
Once you have ran this, you then need to run these:
php bin/magento setup:upgrade;
php bin/magento setup:db-schema:upgrade;
php bin/magento setup:di:compile;
php bin/magento setup:static-content:deploy -f;
php bin/magento indexer:reindex;
php bin/magento cache:clean;
php bin/magento cache:flush;
More information on installing and configuring the tool can be found on the Magento website.
https://devdocs.magento.com/guides/v2.4/migration/migration-tool-install.html
https://devdocs.magento.com/guides/v2.4/migration/migration-tool-configure.html