Hi @Shamrock 
,
Welcome to the forums! Thanks for reaching out. 
If you log in to github, you can revoke the access to your specific repo, if you are troubleshooting the connection between Netlify and Github and want to re-establish it.
In order to remove any published content from Netlify’s servers, you’d need to log in to Netlify and remove the site. Here is a helpful support guide for manual deployment