@florianherzog Thanks for your help. I couldn’t get the first solution working.

I’m trying the second now. I tried creating a new workflow for when the review is created. I set the work flow to:
Thing to change: Current row’s User-company-reviews’s Company
Field: starzvalue (I created this field on the Company data type just for this workflow) = The Company’s User-Company-Reviews:each item’s Star Rating Value: average.

When I create new reviews with this workflow the starzvalue field never updates past 0.

That said, sorting the repeating group with type of content as company is able to be sorted by starzvalue. So once I figure out what’s going on with the data getting into the DB, I think this will work!