My guess would be a general favicon design site. The instructions assume the user is the owner of the site and has access to source HTML. This is not the case for Fandom wikis since Fandom, not the wiki's founder, is the owner of the site. Users must upload the favicon via ThemeDesigner, as TableWiz and Fandyllic mentioned.
I copied and pasted the code that Nintendon't gave me, if you look at the image I put before, that was the original code. So I just copied and pasted the code that that user gave me instead of the original code