so I've kinda of a problem with night shift in my windows copy.

now I've enabled night shift before because i wanted to do a combo with f.lux now I've uninstalled flux and I want to disable night shift too because it has become more of an annoyance. but the option to disable it has been disabled by windows. it's grey and everything. I've already checked with one on r/techsupport and got the answer to update drivers. so I did so. but it's still grey. what I guess is that I've to edit registery but I've no possibility to back up my C disk so I need 100 % work instructions. or should I try something else?