Facebook and Youtube Shooting and Editing

Here's a detailed guide to Auto Reframe from an expert:

https://youtu.be/bfmhuIaFPhA

Basically, Auto Reframe uses aritficial intelligence in Premiere Pro to look at your sequence and change it to another resolution by trying to follow the important action and scaling/shifting to keep it in the frame. It should give you a good start at least and then if adjustments need to be made, the result can be tweaked by the editor. It is designed specifically what you're describing...getting a video to look right on different platforms.

However, there's no guarantee that it will work in every case. If you're using screen recordings, there may or may not be enough change for the AI to find the action. (Don't know what you're recording.) It's worth a shot. Even if you try it and it doesn't give you the desired result, you will at least be able to see what the concept is and how to do it manually yourself. Before auto effects like the came along, that's how everyone did this... 100% manually.