How do I unroot without the proper RUU?

[AC Question]

My HTC one SV has been rooted for awhile and never had any issues, suddenly today it stopped reading sd cards. It is not the sd card as they work in my laptop so something is up. I want to just unroot and revert back to all factory settings as easily as possible because I dont know too much about this process, thing is I read you have to use a RUU with the same version or higher than your current one, and I cant seem to locate one for K2_CL 2.21.0000 they are all 2.06 and under. I tried running it anyway and it fails and says I need the correct utility. How else can I do this? Please help..very frustrated..