"Learn how to add any custom clothing to your Unreal Engine Metahumans. This tutorial covers the essential workflow:
Exporting: Safely export your Metahuman’s body mesh from Unreal Engine.
Conforming: Use Blender to fit your 3D clothing model to the Metahuman’s shape.
Rigging: Bind the clothing to the Metahuman’s armature and apply automatic weight painting for realistic movement.
Importing: Configure the correct export and import settings to bring your finished clothing back into Unreal Engine as a skeletal mesh.
Attaching: Add the custom garment to your Metahuman blueprint so it moves with your character’s animations."
https://dev.epicgames.com/community/learning/tutorials/b6EZ/custom-clothing-for-metahuman-2-0-in-ue5-6-step-by-step