The OBi200 doesn't have a AccessFromWAN option as it doesn't have a built in router like the OBi202 I beleive.
What you need to do is setup port forwarding to point to the OBi200. You say you have done this and it's not working...
First thing to do is go here http://www.whatismyip.com
and make a note of your external IP address, now log into your router by entering it's IP address into your web browser. This is usually something like 192.168.0.1 or 192.168.1.1.
An example... If my router's IP address is 192.168.1.1, my OBi200 IP address is 192.168.1.200 and the port I want to use is 8080 then I would create the following port forward rule on my router:
Make sure you save the changes!
Now enter the IP address you noted down earlier from http://www.whatismyip.com
into your web browser - let's say the IP address you noted down was 126.96.36.199, you would enter 188.8.131.52:8080 into any browser to gain remote access the OBi200.