I have a 6 pins riser.
From my extra CPU (Corsair RM750x) goes to cables (6(2) and a 8 pin) to the GPU (GTX 1080 ti turbo)
How could I Power the riser. One cable is 8 pin(one pin seems empty). Could I put this end in the PSU and the other end 6(2) in the 6 pin riser?

Many thanx for any advise.