The basic steps would be to:
Go to router WebUI -> Network -> Wireless, scan the network and then add the network.
Goto Status -> Routes, in the ARP table you will see all the known IP's, you will have to find the IP address of you hotspot provider. The line with the IP address will have interface name (wlan0).
Get this IP address and enter it into your computer/phone browser and you should be redirected to the hotspot landing page.
If it does not connect, try entering: IP:8443 and maybe then you will be redirected to the loading page. Other than that, it's quite hard to do, as the router is not designed to login to WiFi hotspots