Sign in to Google Tag Manager.
You'll find the Google Analytics Tag in the list of account tags.
Edit the existing tag:
Add a new custom dimension
Then you have to edit the value of the new dimension. To do this, press "new variable".
In the window that appears, choose "Custom Javascript":
In the " Custom Javascript " box , copy the following code:
function () {
var cookie = document.cookie;
if (cookie.indexOf('fstrz=') !== -1) {
return cookie.indexOf('fstrz=true') !== -1 ? 'yes' : 'no';
}
return 'untracked';
}
Then, after saving, you can finalize the creation of the custom variable as below:
Finally, all you have to do is save the tag update and then publish the tag.