There are different ways to get the Accessories, all you need to do is buy them from 2K Store which is a default option or you can earn accessories as rewards by performing different activities on your days off. Sometimes pre-ordered deluxe edition of the game also gets you many different shoes or you can get shoes from endorsements etc. To apply the accessories to your MyPlayer, go to the 2K store and Select accessories. Search for the accessory you want to apply then equip to wear it.