How do I find a Part inside of a few Models?

How would I make a script to go into Models (with different names) and find a Part named "Head" inside them? And then turn them Transparency = 0?

local ting = 0	
owner = script.Parent.Parent.Parent.OwnerName

function onTouched(hit)

	if ting == 0 then -- debounce
		ting = 1 -- debounce
		local check = hit.Parent:FindFirstChild("Humanoid")

		if check ~= nil then -- debounce
			local user = game.Players:GetPlayerFromCharacter(hit.Parent)
			local cost1 = script.Parent.Cost
			local cost = user:FindFirstChild("leaderstats"):FindFirstChild("Dollars")
			local user = game.Players:GetPlayerFromCharacter(hit.Parent)
			
			if (user:FindFirstChild("House") ~= nil) then 
			local user = game.Players:GetPlayerFromCharacter(hit.Parent)
			user.PlayerGui:FindFirstChild("AlreadyOwn").Frame.Visible = true

			elseif user:FindFirstChild("leaderstats").Dollars.Value >= cost1.Value then
				owner.Value = hit.Parent.Name
				cost.Value = cost.Value - cost1.Value	
				
-- the below should find "Head" inside of models of script.Parent.Parent.Parent and make them seen
					for i, v in pairs(script.Parent.Parent.Parent:GetChildren()) do
					if v:IsA("Model") then
					for ii, vv in pairs(v:GetChildren()) do
					if vv.Name == "Head" then
					vv.Transparency = 0
-- finding "Head" ends here

				local own = Instance.new("NumberValue")
				own.Name = "House"
				own.Parent = user
				own.Value = script.Parent.Sell.Value
				local ownshouse = Instance.new("NumberValue")
				ownshouse.Name = "OwnsHouse"
				ownshouse.Parent = user
				ownshouse.Value = script.Parent.Parent.Parent:FindFirstChild("Value").Value
				user.PlayerGui:FindFirstChild("HousePurchase").Frame.Visible = true
				script.Parent.Parent.Ad:remove()
				script.Parent.Parent:remove()
				local home = game.ServerStorage.Home2
				home.Parent = game.Workspace
		
			elseif user:FindFirstChild("leaderstats").Dollars.Value < cost1.Value then
				user.PlayerGui.NotEnough.Frame.Visible = true

			end
		end 


	ting = 0 -- debounce
	
	
	end 			end
					end
					end
					end


end

script.Parent.Touched:connect(onTouched)





This code errors:
Script:33: attempt to index field 'Parent' (a nil value) -- no idea why.

Thats easy! Just use the FindFirstChild function

local Find = workspace.ModelNameHere:FindFirstChild("Head")
if Find then
  Find.Transparency = 0
end