grab a needle-nose pliers hold on one side, and unscrew from the other side.

You will likely need to remove the motherboard with the cooler attached from the case so you can get at the retaining bracket that those screw into. I'm assuming this motherboard is in an older PC case that doesn't have a cutout to access the CPU section from behind it when mounted? Mine is the same way and it can be a right royal pain when you need to change coolers out like this. I had an older Corsair AIO water kit for about 6 years and just changed it out this past summer with a newer corsair AIO kit. Luckily the newer kit still fit using the older bracket from the previous one so I didn't have to remove the motherboard to do this as I had feared.

But yeah, you will need to unhook everything, remove the fan/radiator assembly that the hoses are attached to, and take the mobo and cooling kit out together.

Interesting, my Corsair H90 almost has the same problem - the plastic backplate's hex fittings were rounded out by the nuts after over tightening. You'll be able to get the cooler out by getting to the back of the motherboard and holding the nuts attached to those screws you can't get out.