I am making a Holo Training Place and I need some help,anyone correct me?

For the benefit of people who try to help you in the future, here is what you posted originally, correctly formatted with tags:

game.Players.ChildAdded:connect(function(player)
	player.Chatted:connect(function(chat)
		if player:GetRankInGroup(config.GroupId.Value) >= config.RankId.Value then
			if string.lower(chat) == "SF" then
				if not game.Workspace:FindFirstChild("Thing") then
					game.Lighting.Thing:clone().Parent = game.Workspace
				elseif string.lower(chat) == "close/gf" then
					if game.Workspace:FindFirstChild("Thing") then
						game.Workspace.Thing:Remove()
					end
				end
			end
		end
	end)
end)

Anyway, answering your question:

Has config been declared before the snippet of code you posted for us?

Also, you use string.lower(chat) on line 4 but then you compare it to an uppercase value. That will never be true.

There may be more, but fix these things first, then try to debug a bit yourself, too. Use breakpoints, and the output.

Hope I helped!