Leave feedback for a fanwork. Or multiple fanworks. It can be as simple as I liked this to a detailed list of all the things you loved about the fanwork. The key is to leave some sort of feedback.
If you've already left feedback in the course of a previous challenge, it totally counts. But you're free to leave more feedback.
Afterwards, leave a comment in this post with the equivalent of "I did it!" If you feel so inclined, leave a link to the fanwork you left feedback for so others can check it out.
I tend to do this anyway, but I definitely left a couple of reviews today. However, it was on my phone, so no linking here.