SEO-Attribut image

I am working a website on local computer with the thème Shapely.
I have a problem with the attribut image for the SEO. My plugging SEO Toast tell “The images in this post have no alt text”. Yet I put it in the media in wordpress.
I test with my portfolio with another thème not collorlib and I don’t have this problem.
Could you to try our thème ?
Thank you