Creating custom genre in iTunes 1.2.5.7

How do I create a custom genre?

I have gone through previous answers to this question here but they do not work. There is no "custom" selection in the drop down menu after you are in the "info" section when selecting a song - as stated in a previous answer.

In iTunes selecting "edit" at the Library sidebar brings up the checkable boxes to the left of: "recently added; artists; albums, etc" but other than being able to click the box to the left of these, I can't find anything else to edit - as stated in a previous answer.

So, please, if anyone knows how to do this, please post.

(It is crazy & soooo frustrating because I've created custom genres in the past and it was easily intuitive but that has changed with, I assume, an update.)