How to give players a speedboost once they buy a gamepass?

Here's what I got but I don't know where to put the script or I wrote it wrong because its not working.

I have this script so far:

        local player = game.Players.LocalPlayer
        local id = 479948091
        script.Parent.MouseButton1Down:connect(function()
         game:GetService("MarketplaceService"):PromptPurchase(player, id)
  end)

local passId = 479948091 
local marketplaceService = game:GetService("MarketplaceService")





marketplaceService.PromptPurchaseFinished:connect(function(player,assetId,isPurchased)
if isPurchased then --
    if assetId == passId then 
        game.Parent.Humanoid.Walkspeed=60
                end
         end
end)

I don't know where to put the script. Or if its even right.