You purchase it in-game via the Crown Store. There should be an option for it, which will take you to the Xbox Marketplace to purchase it through Xbox, not ZOS/ESO directly.
If you go in the crown store, on the bottom right hand corner, it says to click in the right stick of your controller to purchase ESO Plus, know that you can only get a one month subscription on Xbox One. That should answer your problem.
I know what you di-Iddly did...(you would be wise not to do that again during a time when Suspicion in the gaming space is at an all time high.)
by not actually revealing real drop tables in the game for all items, you only prove what has been proven with proof of concept that you can/will manipulate item drop chances based on certain elements performed by the player.