Just saw this on Facebook. I received an email in five minutes and have redeemed the game.
Redeeming on PS4 -
Go to PlayStation Store and click on your Avatar at the top of the screen. Select [Redeem Codes] from the drop-down menu. Carefully enter the code and select [Redeem]. The credit or content is now applied to your account.
Redeeming on XB1 -
You can redeem your free NBA 2K20 game via your console or via the web — https://live.xbox.com/redeemtoken
Credit to the poster on Facebook.