The tool is under Weapons > Other > Gravity SWEP. All you gotta do is left click to toggle zero gravity. This toggles zero gravity for any and all props or ragdolls on the map (doesn't affect the player). Doing it a second time will toggle it back off.

Since there isn't any explanation on the description on how the addon works and what I can only assume to be the demonstration video is privated for some reason, hope this short guide helps somebody lol