Proxying between different network cards?

Question

Network administration

Good afternoon guys.

There is a site on IIS. It spins in the domain.
And there is a VPN network between two offices.
You need to move this site to a VPN network.
I decided to do it through NGinx. The proxy works (Inside the domain network by IP anyway), but on the VPN network (there is no DNS server in the vpn network, everything is needed by IP), the site is not visible, and the computer as a whole. As I understand it, this is due to the fact that nginx has two network cards, and routing must be configured somehow. I tried to do it, but unfortunately it didn't work. Did it for the first time, very little experience. Can anyone tell me how to do all this correctly so that access would appear, and is there a problem in routing at all?