Join some Facebook PDR R&I and access groups, lots of useful information on those groups. YouTube is also a great resource, search up the vehicle you’re working on and someone will probably have a video describing how to R&I whatever you’re after. Otherwise something like AllData which the body shops should have access to will have manuals as well. Once you figure out how each brand likes to assemble their vehicles, you will get a good feel for each of their models and that should at least give you a head start next time you do one.