You can watch this gif image to know more about the variant images grouped feature.
This function is meant as categorizing images according to different tags. Example: You have pictures of a white shirt and pictures of a black shirt. When you click on white, only white pictures will be shown instead of both white and black photos that confuse the buyer.
Please follow some instructions below to config it.
Step 1: Go to Product setting and Add tag to images grouped.
Step 2: Go to Theme settings > Product page > Enable "use group variant image"