Allow access from 192.168.1.* to 192.168.2.*

My current network setup looks like this:

Cable Modem/Router (provided by ISP) ---- Router 1 ----------- Router 2
                                          LAN: 192.168.1.1     LAN: 192.168.2.1
                                          Software: OpenWRT    Software: DD-WRT

I want devices connected to Router 1 to be able to access devices on the 192.168.2.* subnet. 192.168.2.X -> 192.168.1.X works, but 192.168.1.X -> 192.168.2.X doesn’t.

How should i do this? Keep in mind i’m a bit of a noob