Asustor NAS setup

Can someone please help me setting up Tailscale on Asustor NAS?
I downloaded Tailscale, set it up, but then somehow I would need to run a command tailscale up --advertise-routes… in ssh but I get response tailscale is not found. I guess it is installed under Docker and I can run docker from ssh, but no clue, how to move on. (also, Portainer CE doesn’t connect either, browser says site can’t be reached. I’m so clueless)