Data Saving, I'm stumped with this problem?

Heres the end of my script, the beginning works good and I go have a pcall in the beginning,

        local ownedCarts = {}
        local getCartData = CartData:GetAsync(player.userId)
        local getCartUpgrade = CartUpgrade:GetAsync(player.userId)
        local folder = Instance.new("Folder",player)
        folder.Name = "CartInfo"
        if getCartData then
            for i,v in pairs(getCartData) do
                table.insert(ownedCarts,v)
                for i = 1,#ownedCarts do
                    local newInt = Instance.new("IntValue",folder)
                    newInt.Name = ownedCarts[i]
                    newInt.Value = 
                end

            end
        else

        end

        while wait(60) do
            StatData:SetAsync(player.userId, {level.Value,coins.Value})
            for i,v in pairs(player.CartInfo:GetChildren()) do
                if v then
                    CartData:SetAsync(player.userId,v)
                else
                    print("Nope")
                end
            end
        end
    end)
end)

So basically what I did is when a player joins it creates IntValues of the Cart Names that they have purchased. I want to keep track of an upgrade that they purchased that goes from 0-5

I have 2 questions,

How do I add a name of the cart to the list of carts that they already purchased in the DataStore

How do I save and connect the upgrades that they purchased to that vehicle?