To use swap effects you have to follow the steps

  • Add an Image 
  • Choose Swap as Image Effect
  • Add an Overlay Image in Style > Overlay > Background Type
  • Change the Hover Effects for both the Image and Overlay Image
  • Use the Transition Duration to adjust the swap speed
  • Now hover over the image to swap between the Image and Overlay

You can also check the below video, for Swap Effects 

Click Here to view some Swap demo