This step assumes that you or one of your teammates has gone through the creating from scratch process. In other words, the initial content and code for a project already exists. You'll know this is the case if you start up your development app and see it in your listing of sites.
In this is the case, go into the builder for that site, then to the site settings. The URL should look something like this:
Click "Import Repo" in the sidebar menu. At this point everything should be good to go.