In order to be able to claim Twitch Drops rewards, you have to make sure that your account is linked to Twitch. From the game account connection page, log in to your game account, then into your Twitch account to link the accounts together. You should not only log in to your Twitch account, but you should also link your game account and your Twitch account by selecting the "Link" icon. Don't forget this step!
To do so, visit our landing page here. Make sure that you watched the correct streamers in order to get your rewards.
Also make sure you have claimed the item from your Drops Inventory. You can find the instructions on how to do this on our website.