Firstly, you'll need to visit the Call of Duty page on Prime Gaming. Next, follow the steps on the website to link your Amazon Prime account to your Activision account. Once this is done, you should see the items in game next time you load up.

One must log into their Amazon account with the Prime subscription to get the redemption code for free rewards. Copy the redeem code. Tap the //callofduty/redemption  and paste the redeem code in the text box.