Ah, now I understand what you mean.
The video is in Equirectangular Projection, which is converted into a 360° video by YouTube. Read more about Equirectangular Projection here.
There is an AfterEffects plugin you can use to convert Equirectangular to Cubic Projection, which is easier to edit. This plugin is called Mettle Skybox.
So there's no easy (and free) way I know of, but this is what worked for me.