If you have a promo code to redeem, follow these steps:
Tap on your player profile icon in the bottom left corner of the main screen
Tap on the Promos option under Community
Enter the Promo Code and submit to receive the Rewards
Code will have to be entered without spaces and all lower case. Copying and pasting will mess up the formatting
Please note that Promo Codes are usually single-use only and can be redeemed once per player account.