Awww... You had me so excited there for a second! I was leaving work, but I had to look up where you found that. I never noticed the "Related Table" section under the "Forms" menu. I clicked on it, and logically, that has to be what they are talking about. There is the list of all all my related forms with checkmarks beside them. I was so happy...
Then, I unchecked them all except one.
And I think we all know how this story ends. . . (spoiler: it didn't do anything, and the checkboxes just reappeared the next time that I clicked "Related Table")