As the title suggests, login on Fanatical, and subscribe to their newsletter in options:
https://www.fanatical.com/en/account?section=contact
*Just in case, subscribe to the Intel newsletter as well, since the e-mail came from Intel ( click on button SIGN UP in right upper corner ):
https://game.intel.com/
You should then (they didnt state when exactly) get an e-mail with the code that you redeem on Fanatical and get the Steam game key. (Click the blue REDEEM CODE button)
E-mail Preview: https://i.imgur.com/2J5cNKD.png
Note: Existing Fanatical (and Intel Access) newsletter subscribers should already receive this e-mail (check junk mail, promo tab, etc.)