Hi Antonio,
Thank you for your interest in the ‘View/edit attributes’ custom widget.
Actually, the hyperlink opens the add-in item in ArcGIS Online. However, to make this widget available for use, add it as an Add-in in to your Operation Dashboard application.
At first, start the Operations Dashboard for ArcGIS Windows application. After that open the operation view in which you want to add this specific widget. Then put the dashboard application in de Edit Operation View mode. Lastly choose Manage Add-ins in menu Widget and search for the ‘view/edit attributes’ item. For more clarification, I have added an overview of this in the attached image.
Just as a reference, you could find more information about custom widgets: Custom add-ins—Operations Dashboard for ArcGIS | ArcGIS. Just as a note Custom add-ins are only available in the Windows application. Nowadays there isn't an software development kit for the html5 browser version.
Hope this helps.
Marco