Mastering Assistant is not on my stereo out channel I have logic 10.7.9

You need Logic 10.8 to have Mastering assisant.

Logic 10.8 works under Ventura or Sonoma so you'd need to update your OS to see the update.

I have Sonoma, and it shows that I have the newest version of Logic. I still cannot see the Mastering Assistant on my computer. (Side note: I do know where to look for it/how to use it).

Add Mastering Assistant to a project in Logic Pro for Mac – Apple Support (UK)