I'm not at home right now but I will try to clarify it.
SSD 1 - Old 860 Evo
SSD 2 - New 860 Evo
HDD
DVD drive
Originally I had Windows 10 running on SSD 1 and HDD with no OS (just data). I unplugged SSD 1, plugged SSD 2 in the same place, installed Windows 10 from a pendrive, tried it...