Click the blue ? in the upper right side of your 1st image. A message will be displayed “To set SSID advanced settings, please click here.” Click the link “here”. You can then enable Layer 2 Isolation locally on your Surf SOHO.
Please note the layer 2 isolation only applies to wireless devices on the same physical SSID radio. An iPhone and a Macbook connected to the same AP will not be able to see each other. However they will be able to see devices in the same subnet connected through an ethernet connection, including devices on other APs. If you require more isolation, you will need to configure additional rules in Advanced > Firewall > Internal Network Firewall Rules.