I recommend that you put miconazole on it and see if it helps clear it up, should see improvement in a few days if it's favus. Here's a link with other ideas:
https://www.backyardchickens.com/t/454373/scaly-skin-on-face-otherwise-happy-and-healthy
https://www.backyardchickens.com/t/454373/scaly-skin-on-face-otherwise-happy-and-healthy