So, let’s say it is Hypnotic Dance Instrument set and you select Synth Pad in the Category list to show only synth pads. Then you accidentally removed Synth Pad category from preset by choosing None in popup menu. Next - deselect Synth Pad from Category list. You will see all presets. Then change order to Category (click on Category tab header to place an order mark (triangle)) and you will see presets without category first. If all your presets has been categorized, then you will see only that one which you just removed from this category. Click right mouse again and select a category. That’s all!