To display one attribute swatches on shop/category pages you need to check the "Enable one attribute swatches on shop/archive pages " checkbox in variation select tab and then select the attribute in next option as shown in the below image. 

You can also upload the hover image for each option of that selected attribute. Once hover image is set , plugin will replace the hover image with product image on swatch hover on shop/category pages. 

If you are using global values as display type make sure you have set hover image for all options for chosen attribute under product/attributes menu.