First, sign-in to your Age Insider Profile. Under Insider Settings, you should see the Steam box. Click the Link Steam button to start linking your Steam account. You should be redirected to a Steam sign-in page similar to the below picture. Click the Sign In button to complete your Steam link.
To unlink your Steam account, click the Disconnect button, and confirm the action from the pop-up.
NOTE: If you have Family View enabled on your Steam account, you will not be able to link your Steam account. Please ensure that Family View is disabled if you want to link your Steam account.