How do I make this model rotate on the proper axis?

I'm trying to make this model rotate normally, as if a table top or something.

function rotateMod(mod,center,rotation)
	local parts ={}
	local function scan(parent)
		for _,obj in pairs(parent:GetChildren()) do
			if (obj:IsA("BasePart")) then
				table.insert(parts,obj)
			end
			scan(obj)
		end
	end
	scan(mod)
	for _,part in pairs(parts) do
		part.CFrame = (center*rotation*(center:inverse()*part.CFrame))	
	end
end
local mod = game.Workspace["Lamp Post"]
local step = 1
repeat wait()
	rotateMod(mod,mod:GetModelCFrame(),CFrame.Angles(0,math.rad(step),0))
until mod == nil

However, I have no idea how to do this. I've never really scripted before so I would have no clue where to start.

Set the primary part, by clicking on the model in workspace and setting it in properties. What the primary part does is basically when it moves the entire model will move in relation to that part.

Now, you can move the entire model around just like you would move a part around using CFrame by using

model:SetPrimaryPartCFrame(cframe)

Using this, you can rotate your model using CFrame. Hope this helped!