You will use the git command, available on all major platforms. For detailed information on this command, consult its documentation or the GitHub cheat sheet. Make sure you have git on the system you'll use to submit your chart.
Run the following command to create a copy of the GitHub repository in your local environment:
git clone https://github.com/openshift-helm-charts/charts/
Then go to your chart's directory under charts/partners/<company>/ to add the material you will submit for certification review.