This theme uses the Jetpack plugin, which can be obtained here or by searching in Dashboard>Plugins>Add New.
Once installed and activated, you will need to sync this with your WordPress.com account. If you don’t have an account there, you’ll just need to create a free account.
You’ll then navigate to Jetpack>Settings>Engagement and then click on the arrow to the right of Sharing to begin editing the Share settings. You’ll verify the settings match the screenshot below.