Select the Character in the scene, click on the "Head" tab at the top and make sure that "Faces" is selected.
This will automatically open the Face folder in the Content Manager, click on the "Custom" tab and then on the + sign at the bottom. Give your "new" head a name and hit the Enter key.
Gerry
System: Win 10 Pro (21H2), Asus X99-E WS, CPU i7-5930K -3,5 GHz, 32 GB DDR4 2666-16 RAM, NVidia GTX 1080 Ti GPU - 11 GB VRAM(Driver Studio-536.99), Samsung 850 Pro 512 GB SSD, 6 TB HD storage.