how do I turn on the radial filter on screen control back on I just get a cross which I have to drag.
Dragging the cross will create you a new radial filter.
If your picture already has a radial filter applied to it, when you click on the radial filter control on the right panel, there will be a circle in the picture at the center of each existing radial filter. Click on the circle to edit it or drag-n-drop the circle to move the filter.