There are a few possibilities to activate your Origin/EA key. You can activate your game key on the Electronic Arts website online or by downloading the EA client app for PC. 

Redeem the key on the EA app:

1. Claim the purchased product on your Kinguin account.
2. Launch the EA client application.
3. Log in to your EA account.
4. Next, open “My Library”.
5. Select “Redeem Code”.
6. Then paste your product in the Activation Key Window.
7. Click “Next” and next “Confirm” 
8. Once you redeemed your code, you can download the game right away or close the window.

Here is a video tutorial on how to activate the Origin/EA key: