The Cubemap Creator is a wizard that when provided 6 different images for the 6 different sides of a cube, will create a cubemap asset for use with Component:Projection360Material.
To create a Cubemap Creator, equip a Dev Tool and while opening the Context menu select Create New, it can be found under the "Editor" tab of that menu.
This only works if all 6 images are provided. If they are not, the wizard will throw an error, which is signified by the button graying out and prompting the user to check their logs.