Routing internet from Win 10 PC to Mikrotik hex PoE

[nepfh]

I have hex PoE, planned to powers few IP cams. I want it to be separated from internet on regular basis and thats easy, since I'm not connecting it directly to internet. The router besides IP cams is connected to second NIC of BlueIris Win 10 PC. The first NIC of PC is connected to main router and thus the machine has access to internet.
However I would like to route sometimes internet to hex PoE from PC's first NIC, to have i.e. firmware update. As I understand, I have to set specific "route ADD" command, but so far with no luck.
Could you guide me how to solve this issue?
I'm adding small network diagram for overview. Thanks!

 

[SouthernYankee]

Your current setup is excellent. Do not change it. You do not want to give the cameras direct access to the internet.
The general rule on camera firmware updates, is only do them when absolutely required to do them when "you have a bug". Cameras are not a PC they do not need to be updated. The most likely thing to happen to a camera when upgrading is that it will turn into a useless brick.
If you really need to upgrade a camera, you download the update file to the PC, then to the camera.

I have 13 cameras on a second nic, I have never upgraded a camera in 3+ years. If it is not broken do not fix it.

Also a good drawing, easy to understand your setup.