if i enable it, it will go back to disabledYou have to look at your motherboard manual or at the asrock forum for step for step instructions.
In general there is going to be a setting in your bios that turns off the iGPU when there is a discreet one,you can change this to leave the iGPU working after that you just run the drivers for the iGPU.
my gpu runs at max mem clock during idle with 2 monitosr, and some people recommending plugging 2nd monitor into mobo, so i thought i might as well try it, since i have 2200g. and im not gonna use my 2nd monitor for gaming or anything like that.As above states, you will have to check your BIOS settings (verify on your MB manual).
However is there any reason why you want to run both when the RX 570 can support up to 5 monitors?