Hi there,
WP Reset was suggested for removing a Site Library import.
But it will remove all Posts, media etc.
If you’re looking to remove an old site library without losing posts etc. then its a manual option of:
1. reseting the GP settings in Appearance > GeneratePress
2. Remove any plugins, posts, pages, media, elements, nav menus, widgets etc that the site import added.
3. Remove CSS from Customizer > Additional CSS
The plus side is the Importer has been updated to make this easier for any new imports you perform:
https://docs.generatepress.com/article/using-the-site-library/#removing-an-imported-site