Default [Q] Remove Root and Tampered Tag

Hi sorry if this is in the wrong section I'm new and couldn't find an appropriate section. I've rooted my phone but have since regretted it. I understand I will not be able to update the phone as I normally would and now the warranty is void. I want to return it back to stock but I'm struggling. I'm trying to s-off it using firewater but when I input adb wait-for-device push firewater /data/local/tmp I get "No such file or directory". Also when I try and delete SuperSU it just comes back (using full unroot option in SuperSU).

Any help is appreciate as I've been struggling for hours and it's really getting me down!