When we experience a trauma, a part of our vital essence of our soul seperates from us in order to survive the experience by escaping the full impact of the pain. (By Sandra Ingerman).
This is called soul loss.
Soul retrieval is recalling those lost parts and intergrate them back in our soul to become whole again.
There are a number of guided meditations on youtube on this subject to be found. Herewith is one I recommend, and which I use a lot.