If you’re using Velo to do this you’ll need to pass the lightbox context data that you can then use to set which image to display within the Lightbox’s code.
Send the lightbox data context when you open it with the data property: https://www.wix.com/velo/reference/wix-window/openlightbox
Get that data context and then use that to set the image you want in the lightbox: https://www.wix.com/velo/reference/wix-window/lightbox/getcontext
If you’re not asking about Velo/JavaScript and this question is about EditorX only then you should ask here: https://www.editorxcommunity.com/