In this video, Tomas Sackmann shares how he transferred the textures and sculpting detail from his original character to a Metahuman using Zbrush, Maya, Mari, Mudbox and Substance Painter.
Zbrush and Zwrap were used to transfer the body geometry to the Metahuman.
Mudbox was used to transfer the textures.
Substance was used to cleanup the texture maps.
Mari was used to remove scars and marks from the original textures.
https://dev.epicgames.com/community/learning/tutorials/1xY4/unreal-engine-transfer-metahuman-textures-from-original-character-overview