Body Bone Mappings

Open the body bone mappings asset and set a skeletal mesh that uses the same skeleton used by the hand bone mappings. Make sure the skeletal mesh faces in the direction of the red arrow in the viewport.

Next press the Auto-fill Bone Mappings button which will bring up a the mappings config window. This window allows to choose from a number of presets such as UE5, UE4 and Mixamo. In this particular example the skeletal mesh being used is roughly based on a UE4 skeleton. Choose the preset that works best for your and make any changes to the config which are required to map all the bones.

As per the hand bone mappings, review that all the auto-assigned bones are correct.

Depending on the skeleton certain bones may be completely missing. If that is the case, press Auto-fill excluded bones.

The head rotation of the skeletal mesh may need to be adjusted, use the head delta to fix the head rotation.