We haven't tested this using a GUI tool like MySQL workbench in a while, but it should work. However the easiest way is to use the CLI - see the
upgrade docs. If you're adding a 2.3 db to a new 2.4 site, then it's important that you run the sql-upgrade task (as outlined in the upgrade docs
here). You'll need to know the mysql username and pass you used when installing AtoM - if you've forgotten, you can look in config/config.php for connection info. When you have done that, rebuild the search index, clear the cache and restart all the services (see
here).