How to start up the Internet through one interface?

Question

linux

Hello colleagues. Straight to the point, I have:
ip address: 192.168.91.4/24 gw: 192.168.91.1 (I go through this interface through a proxy to the Internet + I have access to the local network)
ip address: 172.168.35.99/24 gw: (only provides access to local network)
So the question itself, when I registered the second interface, the Internet disappeared (it tries to connect through the second interface or I don’t understand something), I tried to register the metric (without success). Googled, they write either a masquerade or a nat, tell me how to do it rationally and correctly?
GW:172.168.93.4 (I didn’t comment out this particular gateway, I tried to comment out the gateway from the first interface, so the second interface stops seeing the LAN at all)

Answer 1

Default gw write the correct one.
Something like, I don't remember exactly.
route add default gw IP gateway by default your interface type eth0
Well, in the terminal, write from the admin.
route
And post the results here