How to add alt-text to images in photo grid in Adobe Portfolio?

Hey, I wonder how to add an alt-text to the images in a photo grid on Adobe Portfolio?

Ive searched the web and can only find the option for single images on the web page, but for the images in a photo grid (that displays my portfolio) i only find the option for an image text that is showing on top of the images. 
I want to add an alt-text to help my website SEO and get more traffic. 

How do i do it?