I'm trying to add my column in the advance search to filter down the results. I'm on SharePoint online site as per this link it should be easy. However, when I try to edit the advance search web part I could not find Properties section. Mentioned in the following URL under Point #4.
Please view the image for better understating of my question
It only shows Appearance, Layout and Advanced. But not properties section.
Keep in mind it is SharePoint Enterprise Search Center Sub site. I've also enabled all the features which have search in it.