In this video Tomas Sackmann shares how he transferred the body sculpting details from his original character to the Metahuman body in Maya.
He covers the Maya scene setup for the axis orientation, creating the blendshape for the body, painting weights to avoid seam issues, how to set up the LODs for the body blendshape and how to export this for Unreal.
https://dev.epicgames.com/community/learning/tutorials/DJXe/unreal-engine-creating-a-metahuman-body-morph-in-maya