2. If the main router use 10.0.0.1 as gateway, Change its IP range (in DHCP panel?) from 10.0.0.1 to 10.0.0.200
3. Connect the second router to computer (disable wireless connection on the computer), access the router gui, set to AP mode, disable DHCP service, select Fixed IP address, type in ip address, e.g., 10.0.0.210 (it has to be between 10.0.0.201 to 10.0.0.255), save the setting and reboot the second router
4. connect the second router to the main router (step 1), in a web browser, type in 10.0.0.210. you should see the 2nd router gui.