Setup slightly differs depending on whether you want to use one or mutiple ethernet interfaces for connecting devices in particular subnet. E.g. if you want to connect two devices from subnet 192.168.7.x/24 and two devices from subnet 192.168.2.x/24, then you would have to “partition” your MT router into two parts. Each part would be built off a bridge (something like an ethernet switch), spanning two ethernet ports. If you only wanted to connect one of devices in each subnet at the same time, then you could skip this part.
Then you have to set up router with IP address on each of those subnet devices (either bridge or ethernet port).
The following step depends on whether those devices can use router as their default gateway or not. I’m assuming the IoT gadgets (HMI, PLC, Camera, any devices with Ethernet port) can’t and you’ll have to configure router to perform SRC-NAT on the way from PC subnet towards IoT subnet. Which means that from PC you’ll initiate connection towards gadget’s real IP address. Router will replace PC’s address with it’s own address and gadget will respond to router’s address (which is in the same subnet and hence gadget doesn’t need any routing configuration).
If you need some more concrete advice, then describe your use case more in detail.