Connecting two networks together

I have two separate networks, each connected to the internet with its own router, which acts as a dhcp, and the router has a few devices connected to it.

I also have s server with two NICs which is connected to both routers.

I want to make computers from either network available on the other network.

Can this be done?
I tried “Bridge” the two NICs connections on the server, but that didn’t work, or do I have to have specific setups on the routers before I do that?