Organization where I work has 2 networks i.e. 2 LANs, both are workgroups A & B. Each has its own router that connects to internet directly. 1 LAN cable of 1st router is plugged in switch with many RJ45 ports. I've configured 1st router's DHCP settings from 192.168.1.131 till 192.168.1.255 & the 2nd one from 192.168.1.2 to 192.168.1.129 Default gateway of routers is 192.168.1.1 & 192.168.1.130 respectively. Now problem is that I don't know that when computers are turned on which internet connection will be used by computers. The 1st router or the second one. Is there a way to restrict computers of workgroup A to get internet services from 1st router only & not the other one, if so how. This is important as internet traffic has to be divided network model will be workgroup only.
I'll be very thankful for the reply.

Set the default gateway on the PCs to whatever router you want them to access the internet from.