Hi Jose Ramon,
It would first be good to try to contact your hosting provider and see if the have a recent backup of your website.
Otherwise, if you’re referring to reverting a theme to its original state, you’ll need to remove and re-import it: https://docs.generatepress.com/article/removing-imported-site/
Take note: “The removal process does make changes to your database, so if you have data you don’t want to risk losing, please take a site backup before doing this process.”
Removing a site library theme also removes any customizations added to files created when the theme from the site library was imported.
You may also export/import customizer settings if you prefer through Appearance > GeneratePress.
As mentioned, it would be best to check if your hosting provider has a backup so you could restore your website to its previous state.
It would also be recommended to add a Backup plugin to your WordPress site to avoid instances like this in the future.
Perhaps you’re referring to something else? Kindly let us know if so.
Hope this clarifies. 🙂