[Plugin: Easy FancyBox] How to prevent thumbnail image from being inside gallery?

I’ve tried doing the below from the FAQ (from just after the word NOTE), but to no avail, to prevent thumbnails from showing up inside the gallery. How do I “not attach a photo” to a post in which I’m using that photo?

Any advice?

Thanks!

“C. Right after that starting on a new line, insert all other images you want to show in your gallery. You can even use the WordPress internal gallery feature with the shortcode [gallery link="file"]. NOTE: if the gallery thumbnail is attached to the post, it will be show a second time when flipping through the gallery in FancyBox. If you do not want that, use an image that is not attached to the post as gallery thumbail.”

https://www.ads-software.com/extend/plugins/easy-fancybox/