If you're talking about the name in the calibre library folder, don't look there. Treat it as a black box.
When you send the book to a device or export it, then there are templates you can configure to control the filename.
Sorry! I'm not at a PC so I can't walk you through menus but do take a look at
https://manual.calibre-ebook.com/ especially
https://manual.calibre-ebook.com/template_lang.html which describes templates.
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