This means you’re most likely using an old version.
WordPress.org no longer allowed us to have a save button in the free theme, so we had to remove it and add it to the add-ons.
Go to your account and download a fresh copy of your add-on: https://generatepress.com/account
Then in your WP Dashboard, delete the current version and upload the fresh version.
There should be a save button once you’re using the new version.
Let me know 🙂