IKEA Förhöja wall shelf with drawers, assembly instructions used

Hello, I have bought the used FÖRHÖJA wall shelf with drawers and the one with bins. Now I am wondering how best to attach it under a wall cabinet. Not to the wall, but to the wall cabinet itself, because the previous owners of the kitchen also mounted their FÖRHÖJAs there and the holes are already drilled. Only with screws? Or with screws and nuts for safety?

Hello, do as described in the instructions.

Thank you very much! Let's see if I can make sense of it. :confused: