To add a new deployment key to your Github repository, start by navigating to the Settings tab above your repository browser:
Now click the Deploy Keys tab at the bottom of the settings sidebar:
Next click the Add New Deploy Key button above the list of keys:
Give your new key a name, paste the key from Deploy into the Key field, then click Add Key to save it.
Now navigate back to your Code tab, then copy the Git URL found above the repository browser:
You can now see further information about how to update the repository configuration in Deploy in this article.