You've probably the LAN cable from the 192.168.1.x router connected to the WAN port of the 192.168.2.x router. That adds a firewall which allows machines on the 192.168.2.x network to see machines on the 192.168.1.x network, but not the other way around. If it you want it to work both ways, you need to either:
■assign the computer on the 192.168.2.x network a static IP address, then set up port forwarding for the ports needed for file sharing (135-139 and 445, UDP and TCP for Windows file sharing) on the 192.168.2.1 router to that computer.
■or you need to put everything onto a single network. Disconnect the 192.168.2.1 router, and assign it a static LAN IP address of 192.168.1.2. Disable its DHCP server, and cover its WAN port with a piece of tape. Plug a cable from one of the LAN ports on the 192.168.1.1 router to a LAN port on the 192.168.1.2 router.
If you want two-way file sharing between multiple computers on both networks, you will have to use the second method. Set up user/password access restrictions for security.