either click your character's face in the top left or click on the map in the top right corner, not the little plus or minus icon. it will open either the inventory or a fullscreen map with a little "lottery" treasure chest in the top left. click the chest and there will be a free daily lottery in the bottom left corner. just click the word "free" and you will get the achievement and one of three reward items.
Grimace221 pointed out that if your game crashes when you click it, you can always make another character to have another chance at it.