To redeem the WatchDogs 2 Exclusive Content, please click on this link. Once you access the WatchDogs 2 Exclusive Content website, in the middle of the screen you see "Redeem Your Code".
Once you have clicked "Redeem Your Code" you will be prompted to log in with your Ubisoft account:
Once you have logged in you will be prompted to select your platform of your choice and to enter your code in the field.
Note that the format of the code is as follow: 1231-1231-1231-1231 and that you should also enter hypens between each block of character.
Once the code has been successful, you will see the following confirmation message on the screen.
Note: you also receive an e-mail confirmation, this will be sent to the email address linked to your Ubisoft account.