If you are using flakes to configure your system, add to your nixpkgs overlays attribute (examples will differ, the following is for home-manager):
{
inputs.neovim-nightly-overlay.url = "github:nix-community/neovim-nightly-overlay";
outputs = { self, ... }@inputs:
let
overlays = [
inputs.neovim-nightly-overlay.overlay
];
in
homeConfigurations = {
macbook-pro = inputs.home-manager.lib.homeManagerConfiguration {
configuration = { pkgs, ... }:
{
nixpkgs.overlays = overlays;
};
};
};
}