We are currently working to make the purchase of an ESO Plus membership easier by having it available directly on the Xbox Marketplace. Until that solution is implemented, ESO Plus membership can be purchased by taking the following steps:
•Log into ESOTU with any of your characters
•Press the Menu button
•Select the Crown Store
•Push down on the right analog stick (“Buy ESO Plus”) and accept the prompt to leave the game
You’ll then find yourself within the Xbox Marketplace where you can purchase an ESO Plus membership. After you complete your purchase, log off and restart ESOTU. When you log back in, your membership will be applied to your account!
In a future patch, you’ll be able to simply navigate to the Xbox Marketplace at any time to purchase ESO Plus.