For this to work:
- change router 2's IP to be on the same subnet as router 1 (ie if router 1 is 192.168.1.1 then change router 2 to 192.168.1.2)
- make sure the dhcp server on router 1 isn't going to issue the address that router 2 is using (ie make sure it's range is something like 192.168.1.10 - 192.168.1.254)
- disable the dhcp server on router 2
- make sure the two routers are connect by their lan ports with the wan port on router 2 being empty.
- if they're wifi then make sure they are both setup with the same ssid, passphrase and security settings (eg both wpa2)
That's about it
Of course you could just buy a switch to replace router 2 and save yourself all that trouble