Set 3D animation as Legacy(Debug Menu Grayed Out!)

So I keep reading about animations requiring to be set into legacy mode, and whenever I try to do this I can't edit anything. Not only that, but the option to do it in the first place isn't even there. Why is this such a problem? I need to solve this for a class I am taking.

I click on the Prefab, and the individual clips it self, but the debug menu stays gray.