MetaHuman Extra Tools is a plugin for Autodesk Maya that complements Epic's own MetaHumanForMaya plugin.
With MetaHuman Extra Tools you can:
Export a MetaHuman as a combined mesh that you can edit easily with any application.
Convert your edited meshes to .dna files that you can use inside Unreal to apply the changes to your MetaHuman.
You can see the standard workflow here:
Refer to the Technical Details for instructions on how to install this Maya plugin.