Here you can manage which identity is used to perform Git actions on each space. Git identities are necessary to perform actions on third-party repositories, as well author your commits under your name.
To access this, click on your profile picture at the bottom left of the screen. Then, select User settings and navigate to the Identities tab.
Click on the Add Git Identity button and then select which provided you want to authenticate with.
Click on a row of the git identities list to open its details. From here you are able to search and select spaces that you want to link this identity to.