[Plugin: NextGEN Gallery] can't access enough preview image options

I’m using NextGEN and am editing albums. When I go to the dropdown menu to choose a preview image, I don’t get access to all of the photos I’ve uploaded into the galleries, so the one I need for the specific album isn’t available. I tried going to “Manage Galleries,” finding the photo I wanted, and typing in its title just as the other ones are formatted, but no luck. Without a preview photo, a broken image link appears on the web page. Please help! ??

https://www.ads-software.com/extend/plugins/nextgen-gallery/