Bad root on Galaxy S7 needs unrooting
I had a similar problem and was able to un-root (and later re-root successfully) using the Kingo Android Root (PC Version) which runs in Windows and roots/unroots via a USB cable to the phone with a different process than the on-phone apps.

I hope you were aware before you started that there's always a chance that root will "break" your phone, rendering it useless from then on.  (Hopefully this isn't the case for you.) There are also a lot of downsides to rooting; certain apps and features that become unusable (not the "free for all" I was originally lead to believe.)