Making a gamepass which changes everything to plastic in the game. How do I do this?

I have no experience in scripting, but I am making a tower obby in which everything is made of neon bricks (to make it harder), I'm making a gamepass that makes the entire tower plastic. I have successfully made the script to buy prompt the user to buy the gamepass, but I need to make a script which actually gives the benefits.
I did everything in this vid: https://www.youtube.com/watch?v=FE6-4FKvBsA But I only need the script to make my entire tower to plastic (replacing the walk speed increasing script with my own which changes the entire tower to plastic) I also need to keep in mind about this: https://scriptinghelpers.org/questions/39083/how-would-i-implement-a-complete-iteration-over-the-workspace Thank you so much.

You can have the game pass script inject a LocalScript that will make the textures change only on his end.

local InstanceThatContainsMyParts = workspace.FolderContainingParts

for i,v in pairs(InstanceThatContainsMyParts:GetChildren()) do
	if v:IsA("BasePart") then
		v.Material = Enum.Material.SmoothPlastic
	end
end