I need help when I scroll a mouse, to do a code, any idea?

You can achieve this with UserInputService. Here's an example.

UserInputService has an event called InputChanged that also fires when the mouse wheel is scrolled.

local InputService = game:GetService("UserInputService")

local Forward = function()
	print("The mouse was scrolled forward!")
	-- Do a code
end

local Backward = function()
	print("The mouse was scrolled backward!")
	-- Do a code
end

InputService.InputChanged:Connect(function(Input)
	if Input.UserInputType == Enum.UserInputType.MouseWheel then
		local Direction = Input.Position.Z
		if Direction == 1 then
			Forward()
		elseif Direction == -1 then
			Backward()
		end
	end
end)