your easy and first approach is to use portainer to acces to your dockers webGUI, only need to click on the desired port on container list.
but first time portainer try to open on http://0.0.0.0:yourclickedport that obviosly do not work, so you need to first configure your NAS Ip on:
settings -> enviroments -> local:
after this, the click works as expected and open the desired webGUI.