From VG247: “The Gofannon Forge is now available to reclaim in Destiny 2: Black Armory, but there are a few things you need to do first before you can take it back.
Much like the Volundr Forge, youll need to complete various steps before you can try to reclaim the Gofannon Forge.”
Source: N4G PC Destiny 2: Black Armory – How to unlock and reignite the Gofannon Forge