Installing LineageOS on Samsung Galaxy Tab S2 from Mac

I have a Samsung Galaxy Tab S2 stuck on Android 5.0.2. I wanted to upgrade the software to LineageOS. There is a lot of information out there, but nothing that can help me. A few things first that I need to share. I'm using a Mac. I once unlocked my device and Knox is now void, so it must be unlocked. I can't tell if the bootloader is unlocked. I tried to check using an app, but came back with an error of "Sorry! root access is not properly installed on this device". The tablet is in developer mode, there is no OEM mode or anything like that, and USB debugging is turned on. I have tried several things using Terminal but they didn't work with homebrew and ADB services. These are installed on my Mac. I got as far as trying to add fastboot devices, and it was denied on the terminal, but that probably makes sense if the bootloader is locked. Most instructions imply that you know what to do and don't explain much. Can anyone please assist with step-by-step instructions so I can complete the process of installing LineageOS?