SharePoint 2013 how to set the system master page to default
<p>I have created a custom master page through HTML, and successfully converted to SharePoint master page. I accidentally set the System Master page to this master page as well. I am trying to set the System Master page back to Seattle but I cannot through Master Pages page. (The input fields are missing, some controls are missing). How can I revert the System master page back to Seattle.</p>