I cant figure out how to change a players size by script?

Im trying but I cant figure it out

game.Players.LocalPlayers.Character.Humanoid.HeadScale = #

isn't working for me what is it?

I had a similar problem. The R15 humanoid scaling didn't seem to load in. Try adding them to the humanoid directly

game:GetService("Players").PlayerAdded:Connect(function(Plr)

	Plr.CharacterAdded:Connect(function(Char)
		local Humanoid = Char:FindFirstChildOfClass("Humanoid")

		local HeadScale = Instance.new("NumberValue")
		HeadScale.Value = 1
		
		local BodyHeightScale = HeadScale:Clone()
		local BodyWidthScale = HeadScale:Clone()
		local BodyDepthScale = HeadScale:Clone()
		
		HeadScale.Name = "HeadScale"
		BodyHeightScale.Name = "BodyHeightScale"
		BodyWidthScale.Name = "BodyWidthScale"
		BodyDepthScale.Name = "BodyDepthScale"
		
		HeadScale.Parent = Humanoid
		BodyHeightScale.Parent = Humanoid
		BodyWidthScale.Parent = Humanoid
		BodyDepthScale.Parent = Humanoid

	end)
end)

The values must be there for the model to exist. you are simply missing the Value parameter.

game.Players.LocalPlayers.Character.Humanoid.HeadScale.Value = #