How to add alt text

I've gone through multiple forums, searches, paths, and I can't find any way to simply add alt text to an image in Scene7. The title, description, etc are in the Metadata section but there is nowhere to enter base alt text. Sitecrawlers are showing these images as not having any data on them and as we have thousands of images, it's hurting overall SEO.

Maybe I'm just missing something obvious because this really seems like one of the most simple steps for image optimization but I can not find a straight answer anywhere.