Hi there,
Installing a site from the library should only be done on fresh installations, as it sets new GeneratePress options for you, and installs content/plugins (if you do that step).
During the first step, it generates a backup file of your previous GeneratePress options. To get those back, you would find that file (in your downloads folder or wherever you saved it to) and upload it in “Appearance > GeneratePress”.
Then you would need to go through and delete any content/plugins/media imported by the site.
Let me know if you need more info 🙂