Creating New Rigging to enable for Humanoid Avatar

Heya, folks!
Currently, I’m trying for my second time to make an Avatar. I found a model that I liked, and managed to get it into Unity. From there, I found that the bones were assigned to the wrong parts (chest in the eye spot, arms in the head spot).
I fixed the mapping, but now my goal is to add a new bone for the head in Unity.
I select the circular bone (which I think is a hinge), and then select a new joint (although I’m unclear whether I should do Hinge or Fixed for a head). Regardless, it doesn’t pull up a bone. It adds a new object, but I’m unable to move, re-size, or even see it.

Here’s what I’m looking at. What should I do now?
Thanks for reading!
Stay safe out there!