Every Apple Store has a Genius Room, which repairs everything Apple makes. This union sort of makes sense.

It can get quite sophisticated as all stores are specialized and trained to make these repairs, including Geniuses getting trained on much of the same equipment as an iPhone assembly line, (plus the equipment to do the reverse) including test and validation equipment. I have worked at flagships in top tier cities, down to the smallest mall stores in a market that has exactly one store, the job is exactly the same. These jobs don’t require engineering degrees, but at least for Genius they require quite a bit of training, not so dissimilar from trades. It’s been quite a few years since I’ve been there but used to be if one is promoted up to Genius they will be certified to do repairs. If one fails training and cannot get their Apple Technician Certification, they’re demoted or fired.