How to manually install addon

Go to the "Elder Scrolls Online" folder in your Documents
For Windows: C:UsersDocumentsElder Scrolls Online
For Mac: /Documents/Elder Scrolls Online//
(replace with the client you're using - "live" or "liveeu")
You should find an AddOns folder, if you don't, create one.
Extract the addon from downloaded zip file to the AddOns folder
Log into the game, and in the character creation screen, you'll find the Addons menu. Enable your addons from there.