How to add public packages from github to my .Net solution

I am trying to add packages from https://github.com/orgs/DKE-Data/packages to my asp.net project. Here are the things I have tried

1. Download the package.nupkg file and add the location to the package manager source but it does not allow me to install the package.
2. Add the PackageReference to .csproj file and did a restore - did not work

As these packages are publicly available isn't there a straight forward approach to add them to my packages?

Appreciate any help here!