How do i give someone hd admin if they have premium?

so i want to reward players if they got premium and my script isn't working

it says "attempt to index field 'HDAdminMain' (a nil value)"

game:GetService("Players").PlayerAdded:Connect(function(Player)
	if Player.MembershipType == Enum.MembershipType.Premium then
		_G.HDAdminMain:GetModule("PlayerData"):ChangeStat(Player, "Rank", 2)
	end
end)

also if you can tell me where to put the script that would help