How to add more than one worker in phoenix app?

I want to use MongoDB and ConCaache worker in my app, but when I tried the following

def start(_type, _args) do
    import Supervisor.Spec
    # List all child processes to be supervised
    children = [
      # Start the endpoint when the application starts
      supervisor(MyAppWeb.Endpoint, []),
      # Starts a worker by calling: MyAppWeb.Worker.start_link(arg)
      # {MyAppWeb.Worker, arg},
      worker(Mongo, [[database:
        Application.get_env(:mong, :db)[:name], name: :mongo, pool_size: 100]]),
      worker(ConCache, [name: :my_cache, ttl_check_interval: false])
    ]

I get the following error when running

[info] Application my_app exited: exited in: MyApp.Application.start(:normal, [])
    ** (EXIT) exited in: GenServer.call(:mongo, :topology, 5000)
        ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its
application isn't started
** (Mix) Could not start application my_app: exited in MyApp.Application.start(:normal, [])
    ** (EXIT) exited in: GenServer.call(:mongo, :topology, 5000)
        ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its
application isn't started

What Could I do?