You give it two pictures: a person and an outfit. It returns the person wearing that outfit in the same frame, with the same face, hair, hands, pose and background. Only the clothes change.
Qwen Image 2.1 can already do an outfit swap on its own, but the author counted what goes wrong: of their first 47 swaps about half were unusable, and usually the outfit was not the problem. The camera pulled back to fit the whole outfit in, trousers got pushed into a shot that had no legs, or the whole picture drifted a few pixels so it no longer lined up with the original. The add-on (a LoRA, a small set of extra weights loaded on top of the base model) was trained on swaps corrected by hand to sit on the original pixels. On sixteen swaps it had never seen, the result moved 0.1 pixel from the source instead of 3.6, and the share of face pixels that changed dropped from 14% to under 2%.
It does not draw clothes better than plain Qwen does. Buttons, belts and patterns come out the same with or without it. Its job is to leave the rest of the picture alone.