To understand soul retrieval, it’s first important to understand how a soul can become “lost.”
In soul retrieval, a person is typically guided by an experienced shaman through the process of bringing the lost soul back.
The shaman will reach an altered state of consciousness, go into the unseen realms of spirit, find the soul, and then begin to address whatever it is that caused the soul to fragment. From there, they’ll bring the soul back into this plane.
Of course, there is no scientific consensus on whether humans have souls, or whether they can get lost, no less—but the concept is accepted among shamans and some other spiritual healers.