[Q] How to unroot my GT-N8013 10.1 topic

I more than likely did a lot of unnecessary stuff (newbie here). I recently uninstalled SuperSU to try to get Remote Play app working on my Samsung Note 10.1 GT-28013. Still couldn't get the app to work correctly so I tried unrooting. I opened up the SuperSU app and it stated that no supersu binary was found. Root Checker also stated that I had no root access after this. My idiot self thought that maybe if I factory reset, all would be good.

I factory reset the tablet and tried to update the firmware and it stated that it couldn't due to my device being modified. It is showing the kernel to still be from 2013. Any way to fix this? Help would be much appreciated. If you need more info, just ask!