To get access to the private GitHub repository with the plugin source code please e-mail your Epic Games Marketplace receipt of Logic Driver Pro (Original Logic Driver is also accepted) along with your github username to email@example.com.
This information needs to be verified with Epic Games which may take 1-2 business days or more.
Engine previews, new features, and patches can generally be acquired faster by compiling from source. The repository contains a README with more information on the branch structure. You should already be comfortable compiling a plugin from source.