The router doesn’t have file shares, so it doesn’t show up on file manager. You most likely need to connect to that with a browser by IP-address. But as port forwarding can have severe security issues I really suggest that you learn more on what you’re trying to do and understand the implications before poking holes to your firewall.

I’m not comfortable to provide step-by-step instructions since doing that wrong can cause all kinds of havoc on your network (and the whole apartment if you happen to have IoT-things around).

I did that for a while to try and learn about filtering malicious traffic from the network. Doing that long term would definetly change my life, but very much not in a good way. It’s a endless whack-a-mole game and the winning prize is that your ISP doesn’t give you a call weekly.

It took couple of weeks until the ISP first called and told me that I have malicious traffic coming from my IP. I explained the situation and their representative was very understanding and handled the thing as well as he ever could. I tried to adjust filters, blocklists and all the jazz which was pretty much a full time job already and I still couldn’t make it work on a sufficient level. I got another couple of calls from ISP (again, handled spectaculary considering I was pushing several hundreds Mbps dirty traffic out in the wild) and eventually they just plainly said that they’re forced to kill my connection if situation doesn’t improve. I ran a node without exit for a while but as that’s not a interesting thing to run I eventually shut it down to free resources for more interesting things.

If you have the time and knowledege to do that, I really encourage that, but for me it was too much to keep in the network while trying to maintain some sanity on my everyday life. I firmly believe that my goal of filtering malicious traffic out and keeping an exit node runnig is achievable goal, I just don’t have enough knowledge nor time to gain enough of it to keep exit node running.

And of course there’s legal issues as well and severity of them heavily depends on where you’re living, so really do your homework before doing anything like that.

Yes, that will work. On your router plug in WAN (or whatever that’s called on your router) port to the ISP router, set up IP-range and NAT (plus DHCP and whatever other services you might want to use) and plug in the rest of your network on the LAN side of the router. That way the only thing ISP router will see is your own router and everything else is behind that & yours to configure however you wish.

I’ve ran setup like this on several locations and (if possible) I’ve used bridged port on the ISP router, so that ISP router is only a ‘media converter’ and my own router connects directly to the public internet. Just make sure to have proper firewall configuration and keep safety in mind when doing that. If bridging isn’t possible your traffic just goes trough NAT twice (your router and ISP router) which in some odd edge cases can cause problems, but they’re very rare.