Non-Followers are people whom you follow on Twitter, but who don't follow you back. To access this list from SocialBee, you need to go to your Audience Menu, click on the Non-Followers tab, then select the profile you want to see Non-Followers for.
Since these are accounts that don’t follow you back, are you sure you want to keep them around? We suggest you unfollow them after a while since they are not interested in following your content.
You can go to their profile to unfollow or interact with them or you can add accounts you want to keep following to your whitelist.