Browse to your Active Service.
Hover over the three dots in the top right hand corner of the Service tile in question and click.
Select 'Enable Auto-Renewal' or 'Disable Auto-Renewal' depending on what you are trying to do.
A pop-up box will appear asking you to confirm the change, click accept.
This will bring you to an updated view of the Identity tile, stating that you have opted to automatically renew the subscription.