Once installed, check the Addons menu in. You can install them by copying them to ` \Steam\steamapps\common\left 4 dead 2\left4dead2\addons\`. Choose the custom map or campaign you want to play! For. Select 'Add-on Campaign' from any of the campaign menus. To install maps and mods through the Steam Workshop: How can I install new maps and campaigns on Left 4 Dead 2?I'm a bit tired of the original ones. This guide visually shows you how to install L4D2 custom maps.