Once you do so, you'll see this pop-up confirming that you unlocked the skin:
It may take a little while to sync with Ubisoft Connect but once this has happened, you'll also find the skin unlocked there.
The skin will then be available in-game. It can be equipped for the AR-C rifle in the weapon's customisation menu in Weapon Shops across Hope County.
If you have any questions, feel free to contact us!