You can create an Image Switch effect for any Hover Effects by choosing the first image from Image URL field or Media
For the second image, you can either provide the image tag with src into the Caption field
Or, you can click on the Editor and then Add Media and choose the second image. Make sure to setup the Attachment Display Settings as below.
Then, click Insert into Post button, and click the Insert button.
Please make sure you remove any extra tags. In the caption field, there should be only a single img tag. Remove any extra tags like p.
That’s it. Now it will display a nice image switch effect.