You gain a Bonus equal to the item’s Tier on Wild Arcana and Wylding Lore skill checks.
A number of times per Long Rest equal to the Tier of the item, after you make a d20 roll, you can roll another d20 and choose whether or not to use that instead of the original roll. This effect doesn’t interact with Advantage or Disadvantage - you simply roll a d20 and choose whether to use it instead of the one you already rolled.