If you are using a page builder, you would have to check if you have a way to add a specific class to specific images.
If not, Inspecting your page, it looks like your page builder uses a class wr-element-image On the container of images.
If wanting to scale all images in such containers, you could add a rule like below to Main options > Fonts & Custom > Custom CSS rule box
.is-mobile.home .wr-element-image img {width:50%;}
But that will target images in every container with that class.