Share one computer across my network

Ok so I have two computers on separate networks, Reg and IoT. I want to share a drive between the two computers so I can quickly share large files as the Plex server is on the IoT network. How can I do this? The drive is setup to share if I am on the same network but then it is over WiFi with my PC and to slow.

I tried to setup up a firewall rule to all sharing between the two devices with a Mac address but didn't see anything. See attached image, I have a second one going back the other way.

Any assistance would be appreciated.