As I remember...
In the project directory, you should have the 'Grit' directory. Run 'Build Skin Files.bat'. Open Command Prompt, navigate to the 'image' directory, and run
..\Grit\Build Skin Files.bat
Alternatively, copy the 'images'...
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day