One network sees another, but not vice versa. How to fix?

Question

Network routing

I know little about network administration, so I ask you not to kick much.
An Internet connection is established through router_1 (192.168.1.1) via LAN to the WAN port of router_2 (192.168.3.1).
Devices connected to router_2 see the network of router_1, but not vice versa. The goal is to see the network devices on router_2 through the network devices of router_1.
Router_1 TP-link with open wrt
firmware Router_2 linksys WRT300N with dd wrt firmware

Answer 1

Answer 2

Routes registered?