Select the Sky object, and in the Properties window, assign each image to the corresponding property (e.g., SkyboxBk for back). Creating Custom Skyboxes - Gerald Clark
Drag your six textures into the corresponding slots in the material. Go to Window > Rendering > Lighting .
Extract all files inside skybox.zip to a designated folder on your local machine.
If you are using Unity, follow these steps to turn your images into a functional skybox: