Need urgent help with flashing Samsung S7

[BoostedPenguin]

Hey so.. Phone's root bugged out yesterday and I downloaded twrp and decided I should upgrade it to Android 8.0 then root it. After many hours of failures I managed to flash a 8.0 but I couldn't make the CSC to work, since my phone is region locked to another country so I decided to go back to 7.0 and try again.. but now here it gets complicated because I really don't know what to do. I'm not sure how exactly to go back from 8.0 to 7.0.. Can someone give me detailed steps on what should I do.. I'd be very grateful!