How do you add armor upgrades onto your gear?

I apologize if this has been covered but I am having trouble figuring out how to add armor upgrades to a PC's armor. We found a YouTube video from two years ago that goes through how to use the item forge but when I open items all I see is Armor, Weapons, Templates. There is no Forge listed. Can someone please help us out here?

Thanks.

Click on Templates. You will see the forge button.