You can use the Excel importer to import your large Excel file and then convert your data inside the app into a CSV file via https://marketplace.mendix.com/link/component/108605
This blog provides some extra information too: https://medium.com/mendix/import-export-data-in-mendix-using-csv-module-d3eba261ae49
If you’re really looking for a custom Java action that has an Excel-file (and/or its data) as import parameter and it spits out a .csv-file, I think that’ll be custom development: I don’t see it anywhere. Maybe this will be able to help you write that custom Java-action: https://javacodepoint.com/java-code-convert-excel-file-to-csv-with-apache-poi/
More information on writing your own Java action: https://docs.mendix.com/howto/logic-business-rules/extending-your-application-with-custom-java/
I hope this helps.
If you don’t want to use the Excel export module means, you can achieve this by using custom Java action. Till now there is no JA for your requirement this in market place.