If you can run a cable between the 2 routers then:
Configure the IP address of the secondary router to be in the same subnet as the primary router, but out of the range of the DHCP server in the primary router.
Disable the DHCP server in the secondary router.
Set up the wireless section just the way you would if it was the primary router.
Connect from the primary router's LAN port to one of the LAN ports on the secondary router. If there is no uplink port and neither of the routers have auto-sensing ports, use a cross-over cable. Leave the WAN port unconnected!
If you cant cable connect the you probably will have to use something like this:
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