Your something should probably be config.hardware.nvidia.package.settings.
It’s a bit of an unusual pattern to get at a package via config instead of via pkgs, but this pattern ensures that you get the nvidia-settings associated with the driver you’re using (the equivalent pkgs path is probably pkgs.linuxPackages.nvidiaPackages.stable.settings but anything involving linuxPackages might actually have to be linuxPackages_6_6 or something).
Source: https://github.com/NixOS/nixpkgs/blob/31f91738fb4aae351f1ee93300139c751dcf8196/nixos/modules/hardware/video/nvidia.nix (look for what nvidiaSettings does, then follow the identifier definitions)