If you are referring to the App Studio, you may find more information here. However, I am afraid that there is no Microsoft Visual Studio (VS) Eikon plugin. There is - on the other hand - a flurry of handy tricks implemented in CodeBook, which works a lot like VS. You may find an article on how to access CodeBook here and more information here.
What I think you may be referring to is App Studio .NET SDK, which can be installed using namesake app in Eikon desktop application (provided your Eikon account is entitled for it). Before you install this Visual Studio add-in, you should be aware that App Studio .NET SDK and the whole concept of WPF apps in App Studio are no longer supported.