You will need to copy a public key from the terminal of your DSS user’s account (the account that starts up DSS). To do so, run:
pbcopy < ~/.ssh/id_rsa.pub
Then, add it to the list of accepted SSH keys in your GitHub account. If you do not have a public key generated, you'll need to generate one by running ssh-keygen and following the prompts.
Note, if you are able to clone a github repo from your terminal, then you should be able to connect to an external git repo in DSS.
Detailed documentation can be found in Working with Remotes: https://doc.dataiku.com/dss/latest/collaboration/git.html#setup
Please let us know if you have any questions.