There's no native functionality that allows you to do that in Workflow.
One thing you could try, though, is using the Database plugin to read the file using the ODBC Excel Files driver. With that driver, the XLS is considered a database and each tab is a table. You can then extract each table separately and save them as independent CSVs.
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Technical Product Manager
I don't want to achieve immortality through my work; I want to achieve immortality through not dying - Woody Allen