The menu option to redeem Locker Codes has moved from previous years. This guide will tell you how to enter Locker Codes and get those free in game items.
If you are not at home you can use the MyNBA2K mobile companion app to redeem the code. You will get the ball drop the next time you load up MyTeam on your console or the pack will show up in your packs.
I do not work for 2K, if you encounter a server error when entering the code you can submit a support request to 2K here.