In the top-left menu, click Edit, then open Plugins.
In the Plugins window, search for Procedural First Person and enable it.
You may be prompted to restart the editor after enabling the plugin.
2 - Making plugin content visible
In the Content Browser, click the Settings icon in the top-right.
Enable Show Plugin Content.
After that, the plugin assets will appear under All/Plugins (project plugin) or All/Engine/Plugins (engine plugin), depending on where you installed it.